Greatly improved thermal properties of polybenzoxazine via modification by acetylene/aldehyde groups

Polybenzoxazine Resins with Cellulose Phosphide: Preparation, Flame Retardancy and Mechanisms

Phosphated cellulose (PCF) was synthesized based on urea, phosphated acid and cellulose. The structure of the PCF was confirmed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy coupled with the Energy Dispersive Spectrometer (SEM-EDS). Benzoxazine (Ba)/PCF hybrid materials were fabricated and thermally cured to prepare polybenzoxazine composites (PBa/PCF). The effects of PCF on the curing temperature of Ba were analyzed through differential scanning calorimetry (DSC). The thermogravimetric (TGA) results demonstrated an increased char residue of 50% for the PBa composites incorporating PCF-5% compared with the pure PBa. The peak heat release rate (PHRR) and total heat release (THR) values of the PBa/PCF-5% composites clearly decreased by 58.1% and 16.5% compared to those of the pristine PBa. The smoke released from the PBa/PCF system significantly reduced with the loading of PCF. Moreover, the limited oxygen index (LOI) and vertical burning test level (UL-94) of PBa/PCF-5% reached up to 31 and V0. The flame retardant mechanism of the PCF in the PBa matrix was investigated TG-FTIR and char residues analysis. Finally, the dynamical mechanical analysis (DMA) results demonstrated that the Tg of the PBa/PCF composites was approximately 230 °C, which does not affect further applications of PBa composites.

Propargylamine: an attractive amine source for designing high-performance benzoxazine resins with low polymerization temperatures

A series of benzoxazine resins using propargylamine as the amine source were synthesized to achieve highly thermally stable thermosets with low polymerization temperatures.

Heat-resistant and robust biobased benzoxazine resins developed with a green synthesis strategy

Two high-performance biobased benzoxazine resins from mono-phenols are developed with a green synthesis strategy.

Modification of traditional benzoxazine by blending with polyfunctional benzoxazines containing aromatic group and fluorene group

A series of polyfunctional benzoxazine monomers containing aromatic and fluorene group (AMFB) were used as modified agents to improve the performance of typical bifunctional bisphenol-A-aniline-based (BA-a) benzoxazine resins. The polymerization behaviors of BA-a/AMFB blends were investigated by using the differential scanning calorimetry (DSC), while the dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were used to analyze the thermomechanical and thermal properties of BA-a/AMFB copolymers [poly(BA-a/AMFB)]. Moreover, the cross-section morphologies of poly(BA-a/AMFB) were observed by scanning electron microscope (SEM). The experimental results showed that BA-a monomer has good catalytic activity for AMFB monomers during the curing process. Compared with BA-a polymer [poly(BA-a)], due to the introduction of heat-resistant fluorene ring and the increase of the crosslinking degree of copolymers, the copolymers showed higher glass transition temperature and better thermal properties. For poly(BA-a/AMFB), the T5, T10, and Yc were higher than those of poly(BA-a). With the increase of the alkyl chain length of AMFB monomers, the cross-section creases gradually changed from linear to dendritic, and the number of creases increased significantly, which indicated that the toughness of the copolymers was significantly improved.

A Novel Acetylene-Functional/Silicon-Containing Benzoxazine Resin: Preparation, Curing Kinetics and Thermal Properties

Benzoxazine resin has been paid more attention in the fields of aviation, electronics, automobiles and new energy industries because of its excellent comprehensive performance. Further application is limited, however, by shortcomings such as high brittleness and high curing temperature. Furthermore, higher thermal stability is imperiously demanded in special areas. Incorporating both an acetylene group and silicon into the benzoxazine monomer is a promising possible solution to improve the curing processability, thermal properties and toughness of benzoxazine. In this paper, an acetylene-functional/silicon-containing benzoxazine monomer was prepared by two-step synthesis, and acetylene-functional benzoxazine was also prepared as a comparison. FTIR and ¹H NMR confirmed the molecular structure of acetylene-functional/silicon-containing benzoxazine. Differential scanning calorimetry (DSC) analysis showed that the initial and peak degradation temperatures of acetylene-functional/silicon-containing benzoxazine were decreased by 21 °C and 18 °C compared with acetylene-functional benzoxazine, respectively. The apparent activation energy of the curing reaction of acetylene-functional/silicon-containing benzoxazine was 83.1 kJ/mol, which was slightly lower than acetylene-functional benzoxazine (84.7 kJ/mol). TGA results showed that the acetylene-functional/silicon-containing benzoxazine had a higher thermal stability than acetylene-functional benzoxazine. The temperatures of 5% weight loss of acetylene-functional/silicon-containing benzoxazine were 380 °C in nitrogen and 485 °C in air, and the char yield at 1000 °C was 80% in nitrogen and 21% in air, respectively. The results of mechanical properties showed that the impact strength of acetylene-functional/silicon-containing benzoxazine was higher than acetylene-functional benzoxazine by 35.4%. The tensile and flexural strengths of acetylene-functional/silicon-containing benzoxazine were slightly higher than that of acetylene-functional benzoxazine.

Multifunctional Hybrid Composites with Enhanced Mechanical and Thermal Properties Based on Polybenzoxazine and Chopped Kevlar/Carbon Hybrid Fibers

This work studied the structural, morphological, mechanical, and thermal properties of newly designed polymeric materials using high-performance hybrid fibers to reinforce the polybenzoxazine resins. To achieve this goal, hybrid fibers consisting of chopped Kevlar and carbon fibers were subjected to a silane surface treatment, incorporated into the resin matrix in various combinations, and then isothermally cured using the compression molding technique. The mechanical performances of the prepared composites were scrutinized in terms of bending and tensile tests. By way of illustration, the composites holding 20 wt % Kevlar fibers and 20 wt % carbon fibers accomplished a bending strength and modulus of 237.35 MPa and 7.80 GPa, respectively. Additionally, the same composites recorded a tensile stress and toughness of 77 MPa and 0.27 MPa, respectively, indicating an increase of about 234% and 32.8% when compared to the pristine resin's properties. The thermogravimetric analysis denoted an excellent thermal resistance of the reinforced hybrid composites. Fourier transform infrared spectroscopy proved that the functional groups of the as-used coupling agent were effectively grafted on the external surfaces of the reinforcing systems, and further confirmed that the chemical reaction took place between the treated fibers and the polybenzoxazine matrix, although the scanning electron microscope showed a uniform dispersion and interfacial adhesion of the fibers within the resin matrix. In fact, the incorporation of treated fibers along with their good dispersion/adhesion could explain the progressive enhancement in terms of thermal and mechanical properties that were observed in the hybrid composites.

Safer cables based on advanced materials with a self-healing technique that can be directly powered off and restored easily at any time

A self-healing conductive hydrogel can be used as part of a cable in order for it to be powered off or restored at any time.