Thermal characteristics of epoxy-modified polyurethane and novolac resins composites were investigated by using graphene oxide (GO) functionalized with hyperbranched poly(amidoamine) (PAMAM) as the ...curing component (GOD). The dendritic hybrid curing agent of GOD was synthesized via a divergent method and used to cure epoxy-terminated polyurethane (EPU) and epoxidized novolac resin (ENR). After preparation of the first generation of PAMAM dendrimer by using amino-functionalized GO as the core, Fourier transform infrared spectra, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to prove the successful preparation method of GOD. TGA also showed that thermal characteristics of the hybrid EPU and ENR composites were determined by the amount of GOD and portion of the resins in the composites matrix. The hybrid composites with higher amounts of GOD and ENR matrix showed higher thermal stability and char residue. As example, the ENR-based hybrid composites with 3 wt% of GOD showed char residue of 57.2% at 600 °C and
T
max
of 401.2 °C. In addition, morphological and structural study of the graphitic and hybrid samples was investigated by XRD and electron microscopies.
Protective epoxy coatings, as a result of their inherent brittleness, show insufficient resistance towards initiation and propagation of cracks, which can occur as early as during the curing process. ...To improve premature crack initiation resistance, it is essential to understand the underlying mechanisms. In this work, a solvent-based novolac epoxy, cured with a cycloaliphatic amine, was reinforced with either an epoxypropoxypropyl-terminated polydimethylsiloxane (PDMS), nanoparticles of strontium titanate (SrTiO
3
), or core-shell rubber (CSR) nanoparticles. The effects on coating property transients, curing-induced internal stress, and premature crack initiation susceptibility of the modifier types and CSR (MX 217 and MX 267) concentrations were investigated. In addition, using a digital microscope, the defect and crack morphology in coatings applied to rigid, flat substrates and inner 90-degree angles were characterized. Finally, to evaluate the anticorrosive barrier performance of the reinforced coatings, an electrochemical impedance spectroscopy analysis was employed. Despite a slightly reduced crack initiation susceptibility, the flexible PDMS chains, due to phase separation, resulted in a deteriorated barrier performance. The inclusion of SrTiO
3
nanoparticles also led to a reduced anticorrosion performance, relative to a neat epoxy coating, with a slightly lower crack initiation susceptibility and a minor increase (around 0.2 MPa) in the average internal stress. For 5 wt% MX 217 and MX 267 CSR toughened coatings, the maximum internal stress and crack initiation susceptibility in the series, as well as an associated reduced corrosion resistance, were seen. In spite of a reduction in the elastic modulus, an improved barrier performance and a reduced internal stress and crack initiation susceptibility were observed for 25 wt% MX 217 and 37 wt% MX 267 CSR toughened coatings. To improve barrier properties and avoid premature crack initiation of epoxy coatings, guidelines on modifier selection are provided.
In this work, we discuss the dynamic viscoelasticity of three novolac resins with different molar masses and methylene linkage patterns (para-paravariant prime, ortho-orthovariant prime and ...ortho-paravariant prime methylene linkages) to clarify the relationship between the structure and viscoelastic properties of novolac resins. The linkage patterns of the novolacs were evaluated using 13 C nuclear magnetic resonance spectroscopy. Gel permeation chromatography (GPC) measurements showed that the number density distribution was similar to that predicted for hyperbranched chains. The dependence of the intrinsic viscosity on the molar mass indicated that the three novolacs had a compact branched chain structure similar to that of hyperbranched chains. The glass transition temperatures determined by differential scanning calorimetry (DSC) depended on the molar mass and were less sensitive to the methylene linkage pattern. The viscoelastic spectra obtained by the time-temperature superposition principle for the three resins were similar to each other because the glassy relaxation properties were dominant. Weak polymeric modes originating from the chain connectivity were observed at low frequencies in the composite curve and were well described by the dynamic scaling theory for hyperbranched chains. A clear effect from the linkage patterns on the mechanical properties was not observed.
Polybenzoxazines (Pbzs) are considered as an advanced class of thermosetting phenolic resins as they overcome the shortcomings associated with novolac and resole type phenolic resins. Several ...advantages of these materials include curing without the use of catalysts, release of non-toxic by-products during curing, molecular design flexibility, near-zero shrinkage of the cured materials, low water absorption and so on. In spite of all these advantages, the brittleness of Pbz is a knotty problem that could be solved by blending with other polymers. Chitosan (Ch), has been extensively investigated in this context, but its thermal and mechanical properties rule out its practical applications. The purpose of this work is to fabricate an entirely bio-based Pbz films by blending chitosan with benzoxazine (Bzo), which is synthesized from curcumin and furfuryl amine (curcumin-furfurylamine-based Bzo, C-fu), by making use of a benign Schiff base chemistry. FT-IR and
H-NMR spectroscopy were used to confirm the structure of C-fu. The impact of chitosan on benzoxazine polymerization was examined using FT-IR and DSC analyses. Further evidence for synergistic interactions was provided by DSC, SEM, TGA, and tensile testing. By incorporating C-fu into Ch, Ch-grafted-poly(C-fu) films were obtained with enhanced chemical resistance and tensile strength. The bio-based polymer films produced inhibited the growth of
and
, by reversible labile linkages, expanding Ch galleries, and releasing phenolic species, which was 125 times stronger than bare Ch. In addition, synthesized polybenzoxazine films Ch/Poly(C-fu) showed significant dose-dependent antibiofilm activity against
and
as determined by confirmed by confocal laser scanning microscopy (CLSM). This study suggests that bio-based Ch-graft-polymer material provide improved anti-bacterial property and characteristics that may be considered as a possibility in the near future for wound healing and implant applications.
The Fourier transform infrared spectroscopy of the attenuated total reflection (ATR), solutions and films of a positive diazoquinone-novolac (DN) FP9120 photoresist (PR) are investigated. The bands ...at 966, 1110, 1240, and 1735 cm
–1
, caused by the absorption of the solvent 1-methoxy-2-propyl acetate (MPA), are dominant in the ATR spectra of the PR solution. The solvent is completely removed from the 1.0–5.0-μm-thick PR films during drying at temperatures of ~90°C for 1 hour. It is preferable to detect the residual solvent in solid PR films using the 966 cm
–1
band. The intensity of the vibrations related to aromatic rings (bands in the range 1510–1610 cm
–1
) increases after drying. The band at 1452 cm
–1
is due to the valent vibrations related to the CH
2
bridge between the aromatic rings of phenol-formaldehyde resin and after drying it splits into 2 bands.
Carbon nanotube (CNT) was oxidized to obtain CNTCOOH. Then, furfuryl alcohol (FA) moieties were grafted to convex surface and end caps of CNTCOOH by an esterification reaction to yield CNTFA. CNTFA ...in three different contents was added into novolac resin matrix to improve its carbon yield value and thermal properties. Results from Fourier transform infrared, X-ray photoelectron, and Raman spectroscopies in addition to thermogravimetric analysis showed that CNT was successfully oxidized and modified with FA moieites. Morphological study and dispersion of nanotubes in the novolac resin matrix were studied by scanning and transmission electron microscopies and X-ray diffraction. FA graft content in CNTFA is calculated to be 8.2 %. Also, char value of the novolac resin was increased by 7.1 % by the addition of only 6 wt% of CNTFA.
Short carbon fiber reinforced polymers (CFRP) are successfully prepared by transfer moulding technology. For this purpose, compounds on the basis of novolac/urotropin with different 6 mm chopped ...carbon fibers and silicon powder contents are produced utilizing a laboratory tempered sigma‐blade kneader. These compounds are then shaped into 46 × 8 × 3 mm3 CFRP specimens using a transfer moulding machine. Depending on the material composition, the conversion to C/C‐SiC composites is performed through liquid silicon infiltration (LSI) process or inner siliconization. First, the short fiber content is varied between 30 and 50 wt% and its influence on the process and properties of the composites is studied. Second, an investigation of the inner siliconization through the co‐mixing of silicon powder (1‐23 wt% in CFRPs) during the compound production as well as a comparison with the external silicon infiltration process are presented and discussed. According to the results, the best mechanical properties are achieved at a fiber content of 40 wt% in the case of the external silicon infiltration and at silicon content below 14 wt% for composites produced by the inner siliconization process.
Anionic homo- and copolymerization of
-diethynylbenzene in the presence of n-BuLi in polar solvents was carried out. The use of hexamethylphosphortriamide (HMPA) makes it possible to synthesize a ...completely linear soluble polymer that does not have branching and phenylene fragments. A copolymer of
-diethynylbenzene with diphenyldiacetylene was synthesized. Homo- and copolymers of
-diethynylbenzene have high thermo- and thermo-oxidative stability. By the interaction of side reactive ethynylphenylene groups with various reagents, it is proposed to synthesize clusters along the conducting chain of poly-
-diethynylbenzene. Due to presenting C≡CH side groups, boron, copper, and cobalt derivatives were synthesized. It is shown that not all theoretically possible stereoisomers can be formed as a result of the polymerization. The application of
-diethynylbenzene polymers for the modification of industrial samples of epoxy novolac resin, oligoester acrylates, and carbon fibers has been demonstrated.
A novel fabrication route to make macroporous silicon carbide (SiC) has been proposed in this study. The route is composed of the following two steps: the fabrication of porous α‐SiC/novolac‐type ...phenolic composite using hexamethylenetetramine (HMT) as a curing/blowing agent for the novolac monomer and a conventional reaction‐bonded (RB) sintering of the composite. The α‐SiC/novolac‐type phenolic composite was carbonized at 800°C for 2 h in N2 gas and then reacted with the molten silicon at 1450°C for 30 min under vacuum, resulting in the macroporous RB‐SiC with an open porosity of 48% and relatively large pore size of ~110 μm. The compressive strength of the macroporous RB‐SiC was 113 MPa, which is relatively high compared to those reported for macroporous SiC of equivalent porosities and pore sizes.
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