Tribological and thermal characteristics of epoxy-based composites by incorporating polyaryletherketone

Current research work focuses on the tribological and thermal properties of epoxy resin matrix composites, which were modified by polyaryletherketone (PAEK-C). The results of the infrared spectra and morphologies of fracture surfaces experiments corroborate the successful synthesis of the materials. From the tribological experiments, it can be known that when the mass fraction of PAEK-C was 10 phr., the corresponding composite exhibited the outstanding wear performances, which could be ascribed to the higher H/E ratio. Based on the results of tribological experiments, it could be obtained that the main wear mechanism is governed by combination of the plastic deformation, creation of vertical cracks in the sliding track, separation of debris, and material waves due to adhesions. In addition, the glass transition temperatures ( Tg) and heat-resistance index ( THRI) of the PAEK-C/epoxy resin higher than those of pure epoxy resin matrix, respectively. Furthermore, when the mass fraction of PAEK-C increased, the heat resistance index ( THRI) of the corresponding composite is 196.3°C, which is higher than that of neat epoxy resin (180.9°C). Also, according to the results of thermogravimetric analysis experiments, it could conclude that the activation energy of the curing process is situated in the range of 150–160 kJ mol−1 depending on the mass fraction of epoxy resins.

Melt Processable Novolac Cyanate Ester/Biphenyl Epoxy Copolymer Series with Ultrahigh Glass-Transition Temperature

The rapid progress in silicon carbide (SiC)-based technology for high-power applications expects an increasing operation temperature (up to 250 °C) and awaits reliable packaging materials to unleash their full power. Epoxy-based encapsulant materials failed to provide satisfactory protection under such high temperatures due to the intrinsic weakness of epoxy resins, despite their unmatched good adhesion and processability. Herein, we report a series of copolymers made by melt blending novolac cyanate ester and tetramethylbiphenyl epoxy (NCE/EP) that have demonstrated much superior high-temperature stability over current epoxies. Benefited from the aromatic, rigid backbone and the highly functional nature of the monomers, the highest values achieved for the copolymers are as follows: glass-transition temperature (T_g) above 300 °C, decomposition onset above 400 °C, and char yield above 45% at 800 °C, which are among the highest of the known epoxy chemistry by far. Moreover, the high-temperature aging (250 °C) experiments showed much reduced mass loss of these copolymers compared to the traditional high-temperature epoxy and even the pure NCE in the long term by suppressing hydrolysis degradation mechanisms. The copolymer composition, i.e., NCE to EP ratio, has found to have profound impacts on the resin flowability, thermomechanical properties, moisture absorption, and dielectric properties, which are discussed in this paper with in-depth analysis on their structure-property relationships. The outstanding high-temperature stability, preferred and adjustable processability, and the dielectric properties of the reported NCE/EP copolymers will greatly stimulate further research to formulating robust epoxy molding compounds (EMCs) or underfill for packaging next-generation high-power electronics.

The Effect of Graphene Nanofiller on the Surface Structure and Performance of Epoxy Resin-Polyhedral Oligomeric Silsesquioxane (EP-POSS)

Epoxy resin-polyhedral oligomeric silsesquioxane (EP-POSS) has excellent mechanical properties and hydrophobic properties. In order to adapt for application in sensor and photovoltaic fields, graphene, nano-SiO₂ and nano-ZnO were used to modify EP-POSS. FTIR was used to characterize changes on the surface structure after introducing nanoparticles. The change of hydrophobicity was measured using a contact angle test. TEM test results showed that nanoparticles were successfully inserted between the graphene sheets. However, the content of Si on the surface was low, as the cage structure of POSS in the molecular chain was coated by epoxy groups. XRD tests indicated that nanoparticles facilitated the dispersion of graphene in EP-POSS. XPS characterized the chemical state and content of the elements, confirming that the addition of graphene can induce the enrichment of Si on the surface of EP-POSS, which had a shielding effect on the main chain and improved the hydrophobicity. Wear resistance and adhesion tests showed that, after the introduction of nanoparticles, the EP-POSS coating film met the requirements of graphene materials.

Preparation of hybrid cyanate ester resin in the presence of polysilazane and its properties

A hybrid cyanate ester resin containing polysilazane was prepared via the prepolymerization of bisphenol-A dicyanate ester monomer (BADCy) in the presence of polysilazane (PSZ) under low temperature conditions in a short period of time. Fourier transform-infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy reveal that the polymerization reaction of BADCy can be carried out in the presence of PSZ to obtain a hybrid resin below 100°C and polymethylsilazane (PHS) exhibits an improved prepolymerization effect when compared to polydimethylsilazane (PMS). FT-IR spectroscopy and gel permeation chromatography (GPC) showed that the prepolymerization degree of the PHS/BADCy resin increased upon increasing PHS mass fraction from 0 to 12 wt%, polymerization temperature from 60 to 100°C and polymerization time from 0 to 4 h. The PHS/BADCy hybrid resins samples were prepared and their process properties were investigated by rheometry and Differential scanning calorimetry (DSC). The results indicated that their viscosity was <10 Pa.s in the temperature range of 60–130°C, and the initial curing temperature and curing exothermic enthalpy were 121.9°C and 358.9 J/g, respectively. Furthermore, the cured PHS/BADCy resin possesses excellent thermal and mechanical properties, the 5% weight loss temperature (Td5) and glass transition temperature (Tg) were 424–441°C and 273–282°C, respectively. The cured PHS/BADCy resin with 4 wt% PHS showed the highest flexural strength of 146 MPa and flexural modulus of 4.1 GPa.

Toughening of POSS-MPS composites with low dielectric constant prepared with structure controllable micro/mesoporous nanoparticles

In this work, we developed a modified calcination and extraction method to obtain controllable micro/mesoporous nanoparticle samples POSS–MPS, which were synthesized through glycidyl polyhedral oligomeric silsesquioxane (G-POSS) grafting with aminopropyl-functionalized mesoporous silica (AP-MPS). The POSS–MPS was introduced into the cyanate ester (CE) matrix to optimize the dielectric properties and enhance the toughness of the POSS–MPS/CE nanocomposite. The structure of the hybrid was characterized by FTIR and SEM. The dispersion properties, mechanical properties, dielectric properties and thermal performance were also studied. The results showed that both the C-POSS–MPS and E-POSS–MPS uniformly distribute in the CE matrix with the content of 0.5–4 wt%. The impact strength increased 52% and 60% separately with 2 wt% C-POSS–MPS and E-POSS–MPS addition respectively. The introduction of E-POSS–MPS particles can significantly decrease the dielectric loss value of the POSS–MPS/CE composites to 0.00498, which is of potential in wave transparent composites and structures.

A promising method to improve the performance of CE composites via combining advantages of POSS and MPS.

Thermal and mechanical properties of epoxy blends with a dicyanate ester containing a quinoline moiety

Dicyanate esters (CEs) with a quinoline moiety were synthesized by treating bisphenols with cyanogen bromide in the presence of triethylamine and the structures were confirmed by FT-IR, and NMR spectral studies.

Curing behaviors of cyanate ester/epoxy copolymers and their dielectric properties

The curing behavior and dielectric properties of cyanate ester/epoxy (EP) with a latent initiator imidazole was investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic cure behavior of the blends. Multiheating rate DSC, peak fitting, and iso-conversion method were applied to analyze the curing kinetic parameters. Two distinct peaks were fitted from the dynamic DSC curve and the activation energies of each reaction varied with the increase of curing degrees. Fourier transform infrared spectra revealed that several reactions coexisted during the curing processes of cyanate and EP, resulting in the coexistence of the polymers and copolymers in the final composites. The dielectric properties of the composites were studied and the phenomenon that the dielectric constants for all of the composites are independent of frequency was observed. The thermal decomposition characteristics of the blends were investigated using thermogravimetric analysis. By increasing the content of EP, the thermal properties of the cured blends were improved to a small extent, while the char yield markedly decreased.

Toughening of cyanate resin with low dielectric constant by glycidyl polyhedral oligomeric silsesquioxane

In this article, a high-performance hybrid material was prepared by melt blending from glycidyl polyhedral oligomeric silsesquioxane (G-POSS) and bisphenol-A cyanate ester (CE), using triethylamine as the curing agent. The structure of the hybrid was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM), and the transparency properties, mechanical properties, dielectric properties, thermal performance, and wet fastness were studied. The results showed that G-POSS was uniformly distributed in the CE matrix and could obviously accelerate the curing reaction of the resin. Large amounts of corrugated and scaled structures were observed on the fractures of G-POSS/CE by the SEM photos. When the G-POSS content increased to 7 phr, the tensile strength (75.45 MPa), elongation at break (3.19%), and impact strength (23.76 kJ m−2) reached maximum values, representing increases of 21.75%, 27.6%, and 157.98% relative to that of pure CE, respectively, which indicated that the addition of G-POSS can significantly improve the toughness of G-POSS/CE composites. When the G-POSS content increased to 4 phr, the dielectric constant decreased from 3.27 to the minimum value of 3.05. The heat resistance and wet fastness of G-POSS/CE hybrid materials decreased with increasing G-POSS content.

Synthesis and characterization of optically active polyimides and their octa(aminophenyl)silsesquioxane nanocomposites

New optically active diamine (3,5-diaminophenyl)((R)-3,4-dihydro-1-phenylisoquinoline-2(1H)-yl)methanone was successfully prepared. Optically active polyimides (PIs) were synthesized by reacting the prepared diamine with the aromatic tetracarboxylic dianhydrides, namely, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride/pyromelltic dianhydride by thermal imidization method and characterized using Fourier transform infrared and nuclear magnetic resonance spectral techniques. Additionally, PI nanocomposites were also prepared by incorporating amino-functionalized polyhedral oligomeric silsesquioxane named as octa(aminophenyl)silsesquioxane (OAPS). The cut-off wavelengths of PIs and their nanocomposites were found to be less than 350 nm, indicating that the PIs are transparent. The PIs and their nanocomposites were found to have glass transition temperature between 204°C and 269°C (differential scanning calorimetric analysis). The 10% weight loss temperature and char yield were found to be 319.5–420.3°C and 26.3–62.7%, respectively. The PIs were found to be amorphous as indicated by X-ray analysis. The scanning electron microscopic images of the nanocomposites also reveal uniform distribution of the nanoparticles in the nanocomposite. PIs and PI/OAPS nanocomposites were found to have low dielectric constant in the range of 2.59–3.36.

Thermal and mechanical properties of azomethine functionalized cyanate ester/epoxy blends

A series of azomethine fictionalized cyanate ester and its epoxy blends were prepared and characterized.

Odd–even effect on the thermal properties of Schiff base functionalized dicyanate esters and thermo-mechanical properties of their blends with epoxy resins

An odd–even effect was observed in the case of dicyanate esters described in this work.

Covalent incorporation of aminated carbon nanotubes into epoxy resin network

In order to expand applied field of epoxy resin, its mechanical properties have to be improved. Carbon nanotube (CNT) is regarded as an exceptional toughening agent for polymers. However, poor dispersion quality of CNT in polymer matrix and weak interfacial force between them commonly lead to low reinforcing efficiency. This article presented a study on the mechanical properties of epoxy composite reinforced with aminated CNT (CNT-NH2). The amination of CNT was achieved via a wet chemical procedure using 1,6-diaminohexane (DAH) as amine source. Fourier transform infrared spectroscopy, zeta potential test, and thermogravimetric analysis were employed to investigate the as-prepared CNT-NH2. The results show that DAH has been successfully grafted onto the surface of CNT. Scanning electron microscopic images show that CNT-NH2 is homogenously dispersed in epoxy matrix. Mechanical properties tests suggest that the tensile strength and fracture toughness of the obtained CNT-NH2/epoxy composite are all enhanced compared with cured pure epoxy resin. The tensile strength and fracture toughness of the as-prepared CNT-NH2/epoxy composite with 0.8 wt% CNT-NH2 show 42% and 95% improvement, respectively. These results indicate that CNT-NH2 is a promising toughening agent for enhancing the mechanical properties of epoxy resin.

The study on the compatibility of epoxy resin with liquid oxygen

Lightweight liquid oxygen (LOX) tank has attracted much attention recently, and epoxy resin is considered to be one of the most likely candidate materials. In this work, polymer wafer made from bisphenol-A epoxy resin was firstly treated with LOX, and then its macroscopic morphology, microscopic structure, and chemical composition were analyzed by atomic force microscopy and Fourier transformed infrared spectroscopy. Finally, its compatibility with LOX was studied by mechanical impact test. The results showed that LOX treatment has little influence on the macroscopic morphology and chemical composition of the epoxy resin wafer, but has a large influence on its microstructure and compatibility with LOX. With the increase of immersion time, the surface roughness, the number, length, and depth of the cracks appeared on the sample surface were all increased. The reaction caused by mechanical impact became more frequent and intense. Finally, possible damage mechanism was discussed.