N,N‐dimethylaminopyridine as initiator in the copolymerization of diglycidylether of bisphenol A with six‐membered cyclic carbonates

N,N‐Dimethylaminopyridine (DMAP) was used as initiator to cure mixtures of diglycidylether of bisphenol A (DGEBA) and 1,3‐dioxan‐2‐one (TMC) or 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DMTMC). The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing. We observed the formation of five‐membered cyclic carbonates and anionic carbonate groups that remain unreacted at the chain ends. The formation of these groups was explained by the attack of the anionic propagation species on the methylene carbon of the carbonate group, which leads to an alkyl‐oxygen rupture. By performing the cure in the thermobalance we could evaluate the loss of CO₂ produced in the samples containing carbonates. The kinetics were studied by DSC and analyzed with isoconversional procedures. The addition of carbonates slows down the curing rate. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the materials obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2873–2882, 2006     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of the Curing Mechanism in the GPTS/APTS Binder System

The acid catalyzed sol-gel reaction in the mixed binder system, 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) was investigated and one step and two step synthesis process were compared. Hydrolysis product was observed using the ¹H, ¹³C NMR and Raman spectra. Especially, based on the Raman spectra, epoxy ring opening was observed, varying the ratio of GPTS to APTS. The two step process made clear sol, while the one step process resulted in a milky suspension. According to the Raman spectra, the epoxy ring opening reaction kinetics proceeded slower in the two step process than one step process. Throughout the two step process, it was possible to apply the binder for the coating of substrate.     

Needle-free electrospinning of nanofibrillated cellulose and graphene nanoplatelets based sustainable poly (butylene succinate) nanofibers

Sustainable materials have slowly overtaken the nanofiber research field while the tailoring of their properties and the upscaling for industrial production are some of the major challenges. We report preparation of nanofibers that are bio-based and biodegradable prepared from poly (butylene succinate) (PBS) with the incorporation of nanofibrillated cellulose (NFC) and graphene nanoplatelets (GN). NFC and GN were combined as hybrid filler, which led to the improved morphological structure for electrospun nanofibers. A needleless approach was used for solution electrospinning fabrication of nanofiber mesh structures to promote application scalability. The polymer crystallization process was examined by differential scanning calorimetry (DSC), the thermal stability was evaluated by thermal gravimetric analysis (TGA), while the extensive investigation of the nanofibers structure was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). NFC and GN loadings were 0.5 and 1.0 wt %; while poly (ethylene glycol) (PEG) was employed as a compatibilizer to enhance fillers’ interaction within the polymer matrix. The interactions in the interface of the fillers and matrix components were studied by FTIR and Raman spectroscopies. The hybrid filler approach proved to be most suitable for consistent and high-quality nanofiber production. The obtained dense mesh-based structures could have foreseeable potential application in biomedical field like scaffolds for the tissue and bone recovery, while other applications could focus on filtration technologies and smart sensors.     

Characterization of the molecular deformation behavior of glassy epoxy resins by rheo-optical FTIR spectroscopy

Rheo-optical FTIR spectroscopy was used for the first time to monitor molecular orientation phenomena in highly crosslinked epoxies. After studying the orientation behavior of epoxy/amine networks during uniaxial deformation above their glass transition temperature in a preceding article, this article deals with the rheo-optical characterization of the deformation process of those epoxy systems below T_g. The orientation behavior is influenced by the different molecular structure of the constituents and the free volume entrapped in the resins. Yield strain and tensile modulus are correlated with the slope of the orientation function. The orientation function was found to show an abrupt change of its slope in the yield point region. This phenomenon is discussed with respect to the mechanism of plastic deformation. © 1996 John Wiley & Sons, Inc.     

Effect of aromatic substitution on the cure reaction and network properties of anhydride cured triphenyl ether tetraglycidyl epoxy resins

A systemic study of the impact of aromatic substitution on the reaction rate and network properties of the isomers of a tetraglycidylaniline triphenyl ether epoxy resin cured with anhydride hardeners is presented here. The epoxy resins synthesized in this work were based upon N,N,N,N‐tetraglycidyl bis(aminophenoxy)benzene (TGAPB), where the glycidyl aniline and ether groups change from being all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted epoxy resin (144 TGAPB). Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as glass transition temperatures (T_g) and coefficients of thermal expansion (CTE) both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. Mechanical properties also varied systematically with flexural strength and ductility increasing with increased para substitution, while the modulus decreased. Indeed, the ductility almost doubled, as measured by the work of fracture and displacement at failure highlighting the importance of substitution on properties.     

Ultrasonic properties of transducer backings

For non-destructive testing applications it is often necessary to limit the number of cycles in a pulse produced by ultrasonic transducers. Usually a backing with a high ultrasonic attenuation and with an acoustic impedance chosen to match that of the piezoelectric active element of the transducer is employed. The acoustic properties of the commonly used tungsten/Araldite backings are compared theoretically with those of composites made by pressing tungsten powder with a powder of a plastic metal. The change in ultrasonic velocity and attenuation due to scattering by the tungsten particles is investigated and the dependence on frequency is determined.     

Monitoring real-time curing of epoxies in situ using single-sided NMR

Adhesively bonded joints using epoxy are widely used in aircraft and aerospace structures. Quality control and defect detection during epoxy curing in such applications is critical. We used single-sided nuclear magnetic resonance (NMR) to nondestructively probe and spatially resolve the change in the characteristic NMR relaxation time (T₂) of epoxies during curing on a substrate. Time-dependent T₂ values were fit to a Weibull function to model temporal changes in the NMR measurables. Our results demonstrate that the reduction in molecular mobility of various epoxy/curing agent mixtures occurs more rapidly at the interface than in the bulk. Further use of single-sided NMR to acquire spatially resolved T₂ data will provide a route for elucidatory epoxy curing studies. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 616–623     

Optical Properties of Fullerenated Poly(epoxy propyl carbazole)

Sincethedevelopmentofmethodslformassproductionoffullerenes,therehasbeengTeatinterestinit-Manyresearchgroups'havepaidgreatattentiontothefiJllerene-dopedpolymersinceWang'discoveredinl992thatfullerene-dopedPVKhasanapparentlyincreasingphotoconductivity.WehavereportedthechendcalattachmentofCcocagestothecarbazolegroupsonpoly(epoxypropylcarbazole)(PEPC)chainsbyFriedel-Craftstypereaction'.Here,theopticalpropertiesoffullerenatedPEPCwereinvestigated,whichwillshowitsgoodphotoconductivepropeFtiesbe…     

The pockels coefficient of new polymers for nonlinear optics and its time dependence after poling,compared with dielectric measurements

Epoxy polymers with donor–acceptor type side groups were synthesized for application in nonlinear optics. The stability of the Pockels coefficient was measured in thin films after poling. The relaxation times and their temperature dependence seem to be correlated with dielectric measurements. Guest–host systems (polystyrene and polymethylmethacrylate with dimethylaminonitrostilbene) were investigated for comparison.