Advanced Polybenzoxazine Structures Based on Modified Reduced Graphene Oxide

Synthesis of a Novel Bifunctional Epoxy Double-Decker Silsesquioxane: Improvement of the Thermal Stability and Dielectric Properties of Polybenzoxazine

In this study a new type of bifunctional epoxy compound (DDSQ-EP) based on double-decker silsesquioxane (DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction with dichloromethylvinylsilane, followed by epoxidation reaction of vinyl groups. The resultant structures were confirmed using Fourier transform infrared spectrometry, nuclear magnetic resonance spectrometry and time-of-flight mass spectrometry, respectively. The DDSQ-EP was incorporated into polybenzoxazine to obtain the PBZ/DDSQ-EP nanocomposites. The uniform dispersion of DDSQ-EP in the nanocomposites was verified by X-ray diffraction and scanning electron microscope. The reactions occurred during the curing of the composites and were investigated using infrared spectroscopy of segmented cures. Dynamic mechanical analysis and thermal gravimetric analysis indicated that the storage modulus, glass transition temperature and thermal stability of PBZ/DDSQ-EP were increased in comparison with pure benzoxazine resins. Assessment of dielectric properties demonstrated that the dielectric permittivity and dielectric loss of polybenzoxazine decreased slightly because of the addition of DDSQ-EP.

Polybenzoxazine/carbon nanotube nanocomposites as a polymeric sensing material for volatile organic compounds

The emissions of volatile organic compounds (VOCs) have hazardous effects on humans and the environment, and hence they should be detected and reduced. In this study, polybenzoxazine (PBZ) and amine-functionalized multiwall carbon nanotube (MWCNT) composites were synthesized as a sensor for VOCs. MWCNT were functionalized with two types of diamines, namely, 1,6-hexanediamine (HDA) and phenylenediamine (PDA). HDA or PDA treated MWCNTs were loaded into the benzoxazine matrix with different weight percentages (0.1, 0.3, 0.5, and 1%). FTIR analysis confirmed the chemical attachment of the two types of diamines on MWCNT. XRD diffraction and scanning electron microscopy (SEM) were used to investigate the nanofillers morphology and clarify the differences between pristine and amine-functionalized MWCNT. Thermal gravimetric analysis (TGA) was used to study the composites’ thermal stability and degradation behavior. It was found that, in contrast to neat PBZ, the major degradation temperature of PBZ/0.5%MWCNT-PDA nanocomposites were enhanced by 10%. The electrical conductivity of PBZ was 6.32 × 10–9, which was enhanced to 6.11 × 10–7 in the composites with 1% MWCNT-PDA. This material was tested as a VOCs sensor for methanol, acetone, and toluene and showed that PBZ/1% MWCNT-PDA composite responded to all the vapors.

Electrospun Nanofibrous Membranes Based on Citric Acid-Functionalized Chitosan Containing rGO-TEPA with Potential Application in Wound Dressings

The present research work is focused on the design and investigation of electrospun composite membranes based on citric acid-functionalized chitosan (CsA) containing reduced graphene oxide-tetraethylene pentamine (CsA/rGO-TEPA) as materials with opportune bio-properties for applications in wound dressings. The covalent functionalization of chitosan (CS) with citric acid (CA) was achieved through the EDC/NHS coupling system and was checked by 1H-NMR spectroscopy and FTIR spectrometry. The mixtures to be electrospun were formulated by adding three concentrations of rGO-TEPA into the 1/1 (w/w) CsA/poly (ethylene oxide) (PEO) solution. The effect of rGO-TEPA concentration on the morphology, wettability, thermal stability, cytocompatibility, cytotoxicity, and anti-biofilm activity of the nanofibrous membranes was extensively investigated. FTIR and Raman results confirmed the covalent and non-covalent interactions that appeared between the system's compounds, and the exfoliation of rGO-TEPA sheets within the CsA in the presence of PEO (CsA/P) polymer matrix, respectively. SEM analysis emphasized the nanofibrous architecture of membranes and the presence of rGO-TEPA sheets entrapped into the CsA nanofiber structure. The MTT cellular viability assay showed a good cytocompatibility with the highest level of cell development and proliferation registered for the CsA/P composite nanofibrous membrane with 0.250 wt.% rGO-TEPA. The designed nanofibrous membranes could have potential applications in wound dressings, given that they showed a good anti-biofilm activity against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus bacterial strains.

Innovative Hyperbranched Polybenzoxazine-Based Graphene Oxide-Poly(amidoamines) Nanomaterials

The covalent functionalization of graphene oxide (GO) surface with hyperbranched benzoxazine (BZ) structures has been achieved using poly(amidoamine) dendrimers (PAMAM) of different generations. By increasing the PAMAM generation, multiple benzoxazine rings were synthesized decorating the GO layers. The polymerization process and the exfoliation behavior were investigated. The novel BZ-functionalized GO hybrid materials were characterized by a combination of techniques such as FT-IR, XPS, and 1H-NMR for the confirmation of benzoxazine formation onto the GO layer surfaces. Raman and XRD investigation showed that the GO stacking layers are highly disintegrated upon functionalization with hyperbranched benzoxazine monomers, the exfoliation being more probably to occur when lower PAMAM generation (G) is involved for the synthesis of hybrid GO-BZ nanocomposites. The polymerization of BZ rings may occur either between the BZ units from the same dendrimer molecule or between BZ units from different dendrimer molecules, thus influencing the intercalation/exfoliation of GO. DSC data showed that the polymerization temperature strongly depends on the PAMAM generation and a significant decrease of this value occurred for PAMAM of higher generation, the polymerization temperature being reduced with ~10 °C in case of GO-PAMAM(G2)-BZ. Moreover, the nanoindentation measurements showed significant mechanical properties improvement in case of GO-PAMAM(G2)-BZ comparing to GO-PAMAM(G0)-BZ in terms of Young modulus (from 0.536 GPa to 1.418 GPa) and stiffness (from 3617 N/m to 9621 N/m).

Amino-Functionalized Lead Phthalocyanine-Modified Benzoxazine Resin: Curing Kinetics, Thermal, and Mechanical Properties

Phenol-diaminodiphenylmethane-based benzoxazine (P-ddm)/phthalocyanine copolymer was prepared by using P-ddm resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive. Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA) were used to investigate the curing behavior, curing kinetics, dynamic mechanical properties, thermal stability, and impact strength of the prepared copolymers. The kinetic parameters for the P-ddm/APbPc blend curing processes were examined by utilizing the iso-conversional, Flynn–Wall–Ozawa, and Málek methods. The P-ddm/APbPc blends exhibit two typical curing processes, and DSC results confirmed that the blending of APbPc monomer can effectively reduce the curing temperature of P-ddm resin. The autocatalytic models also described the non-isothermal curing reaction rate well, and the appropriate kinetic parameters of the curing process were obtained. The DMA and impact strength experiments proved that the blending of APbPc monomer can significantly improve the toughness and stiffness of P-ddm resin, the highest enhancements were observed on 25 wt.% addition of APbPc, the recorded values for the storage modulus and impact strength were 1003 MPa and 3.60 kJ/m² higher, respectively, while a decline of 24.6 °C was observed in the glass transition temperature values. TGA curves indicated that the cured copolymers also exhibit excellent thermal stabilities.