Yanchao Yuan

Intumescent flame retardancy of a DGEBA epoxy resin based on 5,10-dihydro-phenophosphazine-10-oxide

5,10-Dihydro-phenophosphazine-10-oxide (DPPA) served as a co-curing agent for 4,4′-diaminodiphenylmethane in the curing reaction of bisphenol A diglycidyl ether (DGEBA) epoxy resin (EP). 1H NMR tracking the reaction of DPPA with DGEBA revealed that the P–H bond in DPPA had a higher reactivity with the epoxy group than the N–H bond. DPPA could promote the curing reaction of DDM with DGEBA. DPPA endowed the epoxy resin with a high flame-retardant efficiency due to the unique combination of phosphorus and nitrogen in the phenophosphazine ring. The cured epoxy resin could achieve a V-0 rating in the UL-94 test with a limiting oxygen index (LOI) of 33.6% at only 2.5 wt% DPPA. The reduced peak heat release rate and total heat release, and increased char yield further verified the excellent flame retardancy of EP. The flame-retardant mechanism of the epoxy resin was investigated by thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscopy, elemental analysis and FTIR spectrometry. The results indicated that DPPA catalyzed the formation of the rigid intumescent char and the generation of the blowing-out effect in the epoxy resin matrix.

Flame retardancy mechanism of poly(butylene terephthalate)/aluminum diethylphosphinate composites with an epoxy-functional polysiloxane

The flame retardancy of poly(butylene terephthalate)/aluminum diethylphosphinate (PBT/AlPi) composites was greatly enhanced by the incorporation of an epoxy-functional polysiloxane (EPM). The limiting oxygen index (LOI), vertical burning (UL 94), and cone calorimeter test were performed to evaluate the flame-retarded effect. The PBT composite containing 11 wt% AlPi attained a V-0 rating of 37.1% in the UL 94 test with LOI and with the aid of 0.6 wt% EPM. The flame-retarded mechanism of the PBT/AlPi/EPM composite was also proposed from the results of the cone calorimeter test, TGA, TGA-FTIR, SEM micrographs, and SEM/EDX analysis of the residues. The introduction of small amounts of EPM greatly encouraged the formation of cross-linking char residue. The condensed-phase action was proposed to be the dominant flame-retardant role of the PBT/AlPi/EPM composite.

Flame–retarded epoxy resin with high glass transition temperature cured by DOPO-containing H-benzimidazole

A halogen-free flame retardant of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-containing H-benzimidazole (DHBI) was synthesized and subsequently used as co-curing agent of 4,4′-diamino-diphenylmethane for diglycidyl ether of bisphenol-A. The structure of DHBI was characterized by Fourier transform infrared (FTIR) spectroscopy, proton, carbon 13 and phosphorus-31 nuclear magnetic resonance, and mass spectroscopy. A series of cured epoxy resins (EPs) were prepared and their flame retardancy, thermal stability, flexibility, and dielectric properties were investigated. The resulting cured EP (EP-10) with 7.45 wt% of DHBI successfully achieved UL 94 V-0 rate with limited oxygen index of 35.6% and without dropping phenomenon. Compared with the cured pristine EP (EP-00), the glass transition temperature of EP-10 was increased by 6.9°C, accompanied with an enhancement of flexible strength by 13.1 MPa and a decrement of dielectric constant by 0.3 at the testing frequency of 1 MHz.

High-performance fluorinated polyimide/pure silica zeolite nanocrystal hybrid films with a low dielectric constant

Pure silica zeolite nanocrystal particles functionalized with aminopropyl groups (APSZN) were introduced into a 2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride-2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl polyimide (FPI) matrix to obtain FPI/APSZN hybrid films. The effect of APSZN content on the hybrid films was carefully evaluated in terms of UV-visible transmittance, dielectric constant (κ), coefficient of thermal expansion (CTE), mechanical properties, dynamic mechanical properties and thermal degradation behavior. The κ of the FPI/APSZN hybrid film decreases to 2.56 with 7 wt% APSZN. With increasing content of APSZN the tensile strength and the Youngs modulus of FPI/APSZN films increase, while the CTE of FPI/APSZN hybrid films decreases. This study provides a novel approach to prepare low-κ FPI hybrids with enhanced properties.

Preparation and properties of a high refractive index optical resin prepared via click chemistry method

PETTA/PETTG optical resin, a kind of LED encapsulating resin with high refractive index, was prepared via click chemistry method in this study. Optical and thermal properties of this resin were investigated with UV–Vis scanning spectrophotometer, Abbe refractometer and thermogravimetric analyses (TGA), respectively. The results show that the light transmitance of this resin can arrive up to 93% and its refractive index is 1.556, which is higher than those of silicone resins. Meanwhile, the cured PETTA/PETTG resin demonstrates the equal thermal stability to silicone resins, and its 5% weight loss temperature was about 350 °C. Therefore, the cured PETTA/PETTG resin could be used as an alternate of expensive silicone resins in LED encapsulation.

Synthesis and characterization of a high refractive diglycidyl ether of thiodibenzenethiol epoxy resin

High refractive index of epoxy resins used as encapsulant in light-emitting diode (LED) is essential in improving the light extraction efficiency, reducing heat and prolonging the service life of LED packages. In this study, diglycidyl ether of thiodibenzenethiol (DGETDBT), an epoxy resin with high refractive index, was synthesized via a novel method and its chemical structure was characterized with Fourier-transform infrared (FTIR) spectrometer and 1H NMR spectrometer. Using m-xylylenediamine (MXDA) as curing agent, the curing behavior of DGETDBT was studied by differential scanning calorimetry (DSC) and was compared with that of diglycidyl ether of bisphenol A (DGEBA), a generally used encapsulant in LED. The thermal behavior and optical performance of these two resins were investigated with thermogravimetric analyses, UV–Vis scanning spectrophotometer, and Abbe refractometer, respectively. The results showed that DGETDBT/MXDA resin demonstrated similar curing and thermal behavior to DGEBA/MXDA resin. But its refractive index reaches 1.698, which is significantly higher than that of DGEBA/MXDA resin (1.604). Comparatively, DGETDBT resin can be expected to be a more effective encapsulant of LED.

Intrinsic Flame-Retardant and Thermally Stable Epoxy Endowed by a Highly Efficient, Multifunctional Curing Agent

It is difficult to realize flame retardancy of epoxy without suffering much detriment in thermal stability. To solve the problem, a super-efficient phosphorus-nitrogen-containing reactive-type flame retardant, 10-(hydroxy(4-hydroxyphenyl)methyl)-5,10-dihydrophenophosphazinine-10-oxide (HB-DPPA) is synthesized and characterized. When it is used as a co-curing agent of 4,4′-methylenedianiline (DDM) for curing diglycidyl ether of bisphenol A (DGEBA), the cured epoxy achieves UL-94 V-0 rating with the limiting oxygen index of 29.3%. In this case, the phosphorus content in the system is exceptionally low (0.18 wt %). To the best of our knowledge, it currently has the highest efficiency among similar epoxy systems. Such excellent flame retardancy originates from the exclusive chemical structure of the phenophosphazine moiety, in which the phosphorus element is stabilized by the two adjacent aromatic rings. The action in the condensed phase is enhanced and followed by pressurization of the pyrolytic gases that induces the blowing-out effect during combustion. The cone calorimeter result reveals the formation of a unique intumescent char structure with five discernible layers. Owing to the super-efficient flame retardancy and the rigid molecular structure of HB-DPPA, the flame-retardant epoxy acquires high thermal stability and its initial decomposition temperature only decreases by 4.6 °C as compared with the unmodified one.

Synthesis and characterization of high refractive epoxy prepolymers with different molecular structures

Three kinds of epoxy prepolymers with high refractive index, diglycidyl ether of thiodibenzenethiol (DGETDBT), diglycidyl ether of thiobis-phenol (DGETP), and diglycidyl ether of oxydiphenol, were synthesized via a two-step method, and the relationship between the chemical structure and refractive index of epoxy prepolymer was discussed. Their chemical structures were characterized using Fourier transform infrared (FTIR) spectrometer and proton nuclear magnetic resonance spectrometer. The curing behavior of all the epoxy prepolymers cured with methylhexahydrophthalic anhydride (MHHPA) was studied using differential scanning calorimetry and was compared with that of diglycidyl ether of bisphenol A (DGEBA). Thermal and optical properties of these cured epoxy resins were investigated using thermogravimetric analyses, ultaviolet–visible scanning spectrophotometer, and Abbe refractometer, respectively. The results showed that three kinds of epoxy prepolymers had the similar thermal property and curing behavior. The sulfur atoms in DGETDBT and DGETP had contributed to an obvious increase in their refractive indexes, while the methyl group in DGEBA cut down its refractive index. The DGETDBT has the biggest refractive index (1.665), followed by the DGETP with 1.612. But the high cost and the lower thermal decomposition temperature of cured DGETDBT/MHHPA resin will limit its application. The refractive index of cured DGETP/MHHPA resin, with preferable thermal stability and acceptable price, is 1.595, which is higher than that of DGEBA/MHHPA resin (1.568). Therefore, DGETP resin can be expected to be a kind of the more effective encapsulant to light-emitting diode.

Preparation and Properties of Halogen-Free Flame Retardant and High Refractive Index Optical Resin via Click Chemistry

Halogen-free flame retardant tri(acryloyloxyethyl) phosphate (TAEP) optical resin was prepared using hydroxy ethyl acrylate (HEA) and phosphorus oxychloride and the chemical structure was characterized by Fourier transform infrared spectrometer and proton nuclear magnetic resonance spectrometer. Optical resins mixed by pentaerythritol tetrathioglycolic and TAEP with different S and P contents were obtained via click chemistry curing. The curing performance, thermal stability and flame retardant performance of the optical resins were analyzed by differential scanning calorimeter, thermogravimetric analyzer, and vertical burning tester, respectively. Additionally, the burned residual morphology of samples was investigated by scanning electronic microscopy, and the refractive indices of the optical resins were measured by an Abbe refractometer. The results revealed that increasing S content could improve the refractive indices of the resins; whereas, the flame retardant performances decreased. The optical resins with S content of 2% and P contents of 7.37% had refractive indices of 1.4935 and UL 94 V-0 flame retard level, respectively. The optical resins had good thermal stability and the 5% decomposition temperature reached up to 200.1 °C.