Jianbing Guo

The influence of hygrothermal ageing on the mechanical properties and thermal degradation kinetics of long glass fibre reinforced polyamide 6 composites filled with sepiolite

In this article, the influence of relatively long hygrothermal ageing on long glass fibre reinforced polyamide 6 (LGF/PA6) composites filled with sepiolite (Sep) are analyzed. The composites with different weight fractions of Sep are exposed in a hygrothermal environment of 80 °C and RH 95% for 0–20 days. The mechanical properties with different ageing time show a decrease in tensile strength and an increase in impact strength. The scanning electronic microscopy (SEM) photos of the impact fracture indicate better adhesion of the interface between the glass fibre and polymer matrix in the composites filled with Sep after the ageing process. Then the thermal stability and degradation kinetics of the composites with different filler fractions and ageing times are studied by thermal gravimetric analysis (TGA) with the methods of Kissinger, Friedman and Flynn–Wall–Ozawa in dynamic measurements. Calculated apparent activation energy (E) by the three methods shows that the composites without Sep have an obvious decrease in the value of E after ageing, however, the E values of the composites filled with Sep have a slight increase.

The effect of thermo-oxidative ageing on crystallization, dynamic and static mechanical properties of long glass fibre-reinforced polyamide 10T composites

The performances and microstructure of long glass fibre-reinforced polyamide 10T (PA10T/LGF) composites that experienced different ageing temperatures (160 and 200°C) with increasing ageing time are characterized by differential scanning calorimetry (DSC), mechanical analysis, thermogravimetric analysis (TGA) and scanning electron microscopy to probe the correlation between properties of the composites and thermo-oxidative ageing. The DSC results show that PA10T/LGF composites occur on degradation, the fracture of molecular chains and the destruction of crystallization structure, which leads to the crystallization and melting peaks of PA10T/LGF composites to shift to high temperature. On the basis of dynamic mechanical analysis data, the reduction of the interfacial bonding between the glass fibre and PA10T matrix and the motion of molecular chain segments result in the thermo-oxidative ageing of composites. According to the calculation of activation energy (E), thermo-oxidative temperature and ageing time can bring about the decline of the E value, proving the deterioration in performance of PA10T/LGF composites. In view of TGA, the increase in the thermo-oxidative temperature and ageing time promotes the degradation of PA10T/LGF composites. The tensile, flexural and notched impact strengths of PA10T/LGF composites decline with prolonging the ageing temperature and time. The surface of materials produces some microcracks and the cross-section surface of PA10T/LGF composites becomes rougher.

The evolution of morphology, crystallization and static and dynamic mechanical properties of long glass-fibre–reinforced polypropylene composites under thermo-oxidative ageing:

In this work, the static and dynamic mechanical properties, crystallization behaviours, and morphology of long glass-fibre–reinforced polypropylene (PP) composites with thermo-oxidative ageing time from 0 day to 50 days at 120°C were investigated and discussed. The static mechanical properties showed a global decrease in tensile, bending and impact strengths with increasing ageing time. From the results obtained by scanning electronic microscopic observations, interface debonding clearly occurred between the glass fibre and PP matrix in the aged samples. The crystallinity (X c) of the composites was analyzed by differential scanning calorimetry; annealing process played the leading role in the early period of ageing, while as ageing progressed, the degradation of PP matrix dominated the ageing process and X c decreased. The dynamic mechanical analysis results indicated that the storage modulus and glass transition temperature of the composites also decreased with prolonging ageing time. Then, the apparent activation energy (E) of glass transition was calculated by the Arrhenius equation with different scanning frequencies. A higher value of E was obtained for the samples in the later ageing period, which means a higher energy barrier for glass transition.

Influence of PA6 as a Charring Agent on Flame Retardancy, Thermal and Mechanical Properties of LGFR PP Composites

Abstract In this work, the combustion, thermal, and mechanical performances of long-glass-fiber-reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) composites with different contents of polyamide 6 (PA6) as a charring agent were investigated by limiting oxygen index (LOI), UL-94 test, cone calorimetry, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and mechanical property test. The results showed that LGFPP/IFR/PA6 composites exhibited much better flame retardancy due to the dense char layer structure, as proved by SEM. When 15 wt% PA6 was added, the LGFPP/IFR composites had the best flame retardancy, and LOI increased by 55.1 %, and the UL-94 reached V-0 rating. The cone calorimeter tests indicated that PA6 could prevent the transmission of heat and the volatilization of flammable substances, thereby reducing the heat release of “second burning”. According to TGA analysis, the carbon layer began to form at a lower temperature due to the synergistic effect between IFR and PA6. Moreover, the calculation of apparent active energy (Ea) revealed that PA6 effectively increased the Ea values of the composites, resulting in a better thermal stability and flame retardancy. In addition, PA6 enhanced the mechanical properties of the composites effectively.

Effect of Brominated Epoxy Resins on the Thermal Stability and Flame Retardancy of Long-Glass-Fiber Reinforced Polyamide 6

Abstract In this work, the compounds of brominated epoxy resins and antimony trioxide (BER/Sb2O3) additives are analyzed and added into long-glass-fiber reinforced polyamide 6 (PA6/LGF) composites in order to solve the “candle-wick effect” caused by glass fibers. The thermal stability, flammability, and morphology of charred residues of the flame retardant PA6/LGF composites are investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and scanning electronic microscopy (SEM). The results show the addition of BER/Sb2O3 provides improvements in flame retardancy by increasing the LOI values, enhancing UL-94 rating, and reducing the heat release rate, total heat release and effective heat of combustion due to the formation of consolidated and thick charred residual structures on the surfaces of the LGF reinforced PA6 composites. When the content of BER/Sb2O3 is increased to 12 wt%, the LOI value and UL-94 rating of BER/PA6/LGF composites reach 24.8 and V-0, respectively. The TGA results exhibit that the decomposition temperature of the PA6/LGF composites decreases with the addition of BER/Sb2O3 additive, resulting in forming some high quality residual char layer. A possible flame retardant mechanism is proposed to illustrate the effect of the gaseous and condensed phases on the flame retardancy of the PA6/LGF composites.