Wei Jen Chen

Tensile creep study and mechanical properties of carbon fiber nano-composites

The surface modification of carbon nanotubes (CNTs) has been recently observed to influence the distribution of CNTs in epoxy resin and the mechanical properties and electrical conductivities of these CNTs. Accordingly, the treatment of multi-walled carbon nanotubes (MWCNTs) with organic acids to oxidize them to generate functional groups on the surface of MWCNTs is a prime task to carry out the surface modification of MWCNTs in this study. This investigation studies the consequent enhancement of their mechanical properties and electrical conductivities. Varying proportions of MWCNTs added to epoxy resin were compared in terms of their effects on mechanical properties such as strength and electrical conductivities of the resulting composites at different temperatures. The test results also indicate that mechanical strength and electrical conductivity increase with the amount of MWCNTs added to the composites. Different coefficients of expansion of the matrix, fiber and CNTs, are such that overexpansion of the matrix at high temperature results in cracking in it. An SEM image of the fracture surface reveals debonding and the pulling out of longitudinal fibers because of poor interfacial bonding between fiber and matrix, which reduce overall strength. Moreover, the creep behaviors of carbon fiber (CF) /epoxy resin thermosetting composites and MWCNTs/CF/ epoxy resin composites were tested and analyzed at different stresses, orientations of fiber, temperatures and humidities. The creep could be classified into two stages: primary and steady-state. The effects of creep stress, creep time, and humidity on the creep of composites containing varing proportions of MWCNTs were investigated at various temperatures. Additionally, creep strain decreased as the number of cycles in cyclic creep tests increased at room temperature and at a high temperature of 55xa0°C. Possible room temperature creep mechanisms have been proposed and discussed. With increasing number of creep tests, the creep strain decreased due to strain hardening which occurred during creep. Creep strain is believed to increase with applied stress, creep time, humidity, temperature and degree of the angle θ between the orientation of the fiber and the direction of the applied stress. The decrease in creep strain of CF/epoxy resin composites was also investigated after aging pretreatment in a constant temperature and humidity chamber for varying durations before creep testing. Finally, the Findley power law was used to fit the curves for creep strain in the CF/epoxy resin composites and MWCNTs/CF/epoxy resin composites under various test conditions.

Electrical and Mechanical Properties of Carbon Aerogels / Phenolic Resin for Nanocomposites

This study used carbon aerogels (CA) and phenolic resin in fixed proportations to produce nano high polymer resin, and used poly ehtylene oxide (PEO) as the modifying agent for phenolic resin to improve the mechanical properties of phenolic resin and promote the surface conductivity. The prepared nano high polymer resin and carbon cloth were made into nano-prepreg by using ultrasonic impregnation method, and a nano-prepreg composite material was prepared by using hot compacting and cut to test pieces to measure its mechanical properties and surface conductivity as well as the influence of temperature-humidity environment (85°C/168hr and 85°C/85%RH/168hr) on mechanical properties. The result showed that the surface conductivity increased by 64.55%, the tensile strength at room temperature increased by 35.7%, the flexural strength increased by 18.4%, and the impact strength increased by 101%. In hot environment (85°C/168hr), the tensile strength decreased by 23.8%, the flexural strength increased by 3.1%, and the impact strength increased by 84.6%. In high temperature-high humidity environment (85°C/85% RH/168hr), the tensile strength decreased by 29.6%, the flexural strength decreased by 17%, and the impact strength increased by 95.7%.Introduction

Study on the Mechanical and Electrical Properties and Creep Behaviour of Carbon Fiber Nano-Composites

In recent years, the influence of surface modification of carbon nanotubes (CNTs ) on CNT’s dispersion among epoxy resin, mechanical properties and electrical conductivities of CNTs has been observed. On account of above-mentioned effects, that CNTs treated with oxidizing in organic acids, a kind of surface modification, generates functional groups on the surface of CNTs is a major investigation in this study to enhance mechanical properties and electrical conductivities of CNTs. In this study, CNTs dispersed among epoxy resin well by adopting ultrasonication method and then the nano-prepreg was fabricated by mixing CNTs/Epoxy resin into carbon fiber. The influence of the different proportion contents of CNTs added into Epoxy resin on mechanical properties and electrical conductivities of composites is investigated. The strength of material tested under different circumstance is also observed. Furthermore, the creep behavior of carbon fiber/epoxy resin thermosetting composites tested under different circumstance and stress is also concerned to be analyzed.

Creep Behavior Study for Carbon Fiber Nano-Composites

The surface modification of carbon nanotubes (CNTs) has been recently observed to influence the distribution of CNTs in epoxy resin and the mechanical properties and electrical conductivities of these CNTs. Accordingly, the treatment of CNTs to with organic acids to oxidize them generates functional groups on the surface of CNTs. This investigation studies the consequent enhancement of the mechanical properties and electrical conductivities of CNTs. The influence of adding various proportions of CNTs to the epoxy resin on the mechanical properties and electrical conductivities of the composites thus formed is investigated, and the strength of the material is tested at different temperatures.The test results also indicate that mechanical strength and electrical conductivity increase with the amount of CNTs added to the composites. Different coefficients of expansion of the matrix, fiber and CNTs, are such that overexpansion of the matrix at high temperature results in cracking in it.Moreover, the creep behaviors of carbon fiber (CF) /epoxy resin thermosetting composites and CNTs/CF/ epoxy resin composites were tested and analyzed at different stresses, orientations of fiber, temperatures and humidities. The creep exhibits only two stages-primary creep and steady-state creep. The effects of creep stress, creep time, and humidity on the creep of composites that contain various proportion of CNTs were investigated at various temperatures.Additionally, increasing the number of cycles in cyclic creep tests at room temperature resulted in a decrease in creep strain even at a high temperature of 55°C. Possible room temperature creep mechanisms have been proposed and discussed. With increasing number of creep tests, the creep strain decreased due to strain hardening which occurred during creep. Creep strain is believed to increase with applied stress, creep time, humidity, temperature and degree of the angle θ between the orientation of fiber and the direction of the applied stress.Finally, the test results of creep strain of CF/epoxy resin composites and CNTs/CF/epoxy resin composites tested under various conditions can be smoothly fitted by the fitting curves of Findley power law.

Mechanical Properties and Creep Behavior of Carbon Fiber Nano-Composites

Recently, it has been observed that surface modification of carbon nanotubes（CNTs）influences on CNT’s distribution among epoxy resin and affects the mechanical properties and electrical conductivities of CNTs. Owing to above-mentioned effects, carbon nanotubes treated with oxidizing in organic acids, a kind of surface modification, generates functional groups on the surface of CNTs taht is a major investigation in this study to enhance mechanical properties and electrical conductivities of CNTs. The influence of the different proportion contents of CNTs added into epoxy resin on mechanical properties and electrical conductivities of composites was investigated, and strength of material tested under different temperature environments was observed. Moreover, the creep behavior of carbon fiber（CF）/epoxy resin thermosetting composites tested under different temperature and stress were also concerned to be analyzed. The resulting creep behavior consists of only two stages, including primary creep and steady-state creep. The effects of creep stress, creep time, different humidity treatment on the various temperature creep of composites containing different proportion contents of CNTs were investigated. It is believed that the increased creep strains can be attributed to higher applied stresses, longer creep times, higher humidity, higher temperature and lower hardnesses. The test results also exhibit that mechanical strength and electrical conductivity increase with the increase of CNTs content added into composites. In the influence of temperature effect on specimen, because of different coefficient of expansion among matrix, fiber and CNTs, the overexpansion of matrix caused by high temperature results in crack occurred among matrix. From observation of the fracture surface by SEM image, the debonding occurs and longitudinal fibers are pulled out due to poor interfacial bonding of fiber and matrix, which also results in entire strength degeneration.

Creep Behavior and Mechanical Properties of Carbon Fiber Nano-Composites

In recent years, it has been observed that surface modification of carbon nanotubes（CNTs）influences on CNT’s distribution among epoxy resin and affects the mechanical properties of CNTs. Accordingly, the treatment of CNTs to with organic acids to oxidize them generates functional groups on the surface of CNTs. This investigation studies the consequent enhancement of the mechanical properties of CNTs. The influence of adding various proportions of CNTs to the epoxy resin on the mechanical properties of the composites thus formed is investigated, and the strength of the material is tested at different temperatures. The creep behaviors of carbon fiber (CF) /epoxy resin thermosetting composites and CNTs/CF/ epoxy resin composites were tested and analyzed at different stresses, orientations of fiber, temperatures and humidities. The creep exhibits only two stages- primary creep and steady-state creep. The effects of creep stress, creep time, and humidity on the creep of composites that contain various proportion of CNTs were investigated at various temperatures. Additionally, increasing the number of cycles in cyclic creep tests at room temperature resulted in a decrease in creep strain even at a high temperature of 55°C. Possible room temperature creep mechanisms have been proposed and discussed. With increasing number of creep tests, the creep strain decreased due to strain hardening which occurred during creep. Creep strain is believed to increase with applied stress, creep time, humidity, temperature and degree of the angle θ between the orientation of fiber and the direction of the applied stress. Moreover, the test results of creep strain of CF/epoxy resin composites and CNTs/CF/epoxy resin composites tested under various conditions can be smoothly fitted by the fitting curves of Findley power law. Finally, the test results also indicate that mechanical strength increase with the amount of CNTs added to the composites. Different coefficients of expansion of the matrix, fiber and CNTs, are such that overexpansion of the matrix at high temperature results in cracking in it. An SEM image of the fracture surface reveals debonding and the pulling out of longitudinal fibers because of poor interfacial bonding between fiber and matrix, which reduce overall strength.

Environmental Effects on Mechanical Properties of Modified and Unmodified Carbon Nanotube/Epoxy Resin Nanoomposites

The composites of mechanical and thermal properties of modified and unmodified Carbon nanotube /epoxy resin nanocomposites tested under various circumstances is a major investigation in this study. Identification of functional groups of CNT surface using Fourier transforms infrared spectroscopy (FTIR) was done to male sure if the means of modification adopted in this study is successfully. The tensile and flexural strengths of modified CNT-containing nanocomposites with the amount of modified CNT around 0.75 Phr tested under room temperature circumstance increase 10.96 % and 21.44 % respectively. These two strengths of nanocomposites tested under high temperature circumstance increase 14.55 % and 10.80 % respectively. Additionally, both strengths of nanocomposites tested under high temp.-high humidity circumstance increase 11.65 % and 23.53 % respectively. According to the test results using pyris diamond thermomechanical analyzer (TMA) coefficient decreases 39.81 % with increasing the content of modified CNT and meanwhile glass transition temperature increases 4.15 %. Because of above-mentioned effect, a modified CNs-containing nanocomposite possesses great thermo stability. Overall, No matter what circumstance (high temperature or high temp.-high humidity circumstances) nanocomposites expose to, and no matter whether CNT are modified or not, CNT do significantly enhance mechanical and physical properties of composite.

Preparation, Characterization and Thermal Properties of Green Polypropylene/Intumenscent Flame Retardant Composites

Polypropylene (PP) has the disadvantage of flammability and easy dripping, flame retardant was incorporated into polymer to improve the thermal and flame retardant property. Conventional flame retardant containing halogen would release toxic gases when the materials got fire and let the people died in the fire and destroy the environment. Intumenscent flame retardant consists of three key components: acid source, carbon source and blowing agent. Acid source is phosphoric acid, which can dehydrate the materials. Carbon source can form char layer to prevent further thermal degradation. The blowing agent can swell the carbon layer to avoid heat and mass transfer during material get fire. Novel intumenscent flame retardant which contains phosphorus and nitrogen was successfully prepared. FTIR, TGA, LOI and UL-94 were used to characterize the structure, flame retardant mechanism and thermal property of the composites. LOI and UL-94 data showed the composites possess excellent flame retardant property. For kinetic of thermal degradation.