Mu Huo Yu

Study on the Chemical Modification of Cellulose in Ionic Liquid with Maleic Anhydride

Dissolution and regeneration of cotton cellulose using ionic liquids as solvent was investigated. In this paper, modification of celluloses with maleic anhydride (MA) was carried out in ionic liquid,1-allyl-3-methylimidazolium chloride(AmimCl).The maleylation celluloses with degrees of substitution (DS) between 0.85and 1.46 were accessible in IL. The effects of reaction time, temperature and mass ratio of the MA in cellulose were investigated. These maleylation celluloses were characterized by infrared spectroscopy, thermogravimetric analysis (TGA). Experiments showed that the optimal conditions for grafting were: mass ratio of maleic anhydride and cotton cellulose 0.8; reaction time of 90 min; temperature of 80 °C.

Effect of Tension on Mechanical Properties and Structure of Aramid Fibers during Heat Treatment

The heat treatment was carried out to modify the aramid fibers, and the effect of tension on the mechanical properties and structure was investigated through Fiber Strength Equipment, viscosity, XRD and SEM . The results show that fibers，strength slightly decrease, but modulus increase significantly according to the increasing of tension at 480°C and 10s, and reach a maximum when the tension value is 300 g. After heat treatment, molecular weight decrease and the degree of crystallinity increase. SEM show that there is little effect on the surface topography of the fibers during treatment.

Rheological Behaviors of Polyacrylonitrile Melt Using Ionic Liquids as a Plasticizer

The rheological behaviors of polyacrylonitrile/ionic liquids (PAN/ILs) melt were investigated to determine the general processing parameters and offer an important theoretical foundation of plasticized melt spinning. A step was carried out to decide the accurate temperature through the temperature sweep and time sweeps. The impacts of the concentration and temperature on the modulus of PAN/ILs samples were studied by dynamic sweeps. The three-parameter Carreau viscosity model was used to predict the zero-shear viscosity from the apparent viscosity data. The PAN/ILs melt showed shear-thinning behaviors. The melt with higher PAN concentration was found to be more sensitive to the temperature. However the structural viscosity index of the melt first decreased and then increased with the increase of temperature.

N-Alkyl PPTA: Preparation and Characterization

N-alkyl poly(p-phenylene terephthalamide)s (PPTA) is synthesized from PPTA and bromoalkane via metalation process in a solution of potassium methylsulfinylcarbanion in dimethyl sulfoxide. The modified PPTAs have been dissolved in conventional solvents, such as THF and CHCl3. The effects of substituted alkyl, substitution degree and inherent viscosity of PPTA on the solubility of N-alkyl PPTA were discussed. The substitution degree is calculated by FTIR and NMR. The molecular weight and distribution of N-alkyl PPTA has been obtained by GPC. The thermal properties are also discussed.

Effect of Sodium Citrate on Electrochemical Behaviour of Copper in Acid Bath

The initial stages of copper electrodeposition in acid copper sulphate/sodium citrate bath were investigated with varying copper and sodium citrate concentrations. Different electrochemical measurements, including linear sweep voltammetry, cyclic voltammetry, and chronoamperometry were introduced to the study. The Scharifker-Hills model was introduced to identify the nucleation model with analysing current transients. It was observed that the increase of copper ions inhibited the cathodic polarization behaviour for the reduction of ions. On the contrary, sodium citrate promoted the cathodic polarization behaviour. The chronoamperometry results indicated that without the sodium citrate, the nucleation process corresponded to instantaneous nucleation and three-dimensional diffusion limited growth, although obvious deviations were observed. While the addition of sodium citrate changed the deviations and caused that the initial deposition kinetics followed well with the mechanism of instantaneous nucleation.

Electroplating of Copper on the Continuous Carbon Fibers

Surface metallization of continuous carbon fibers (CFs) can improve the properties of the interface between the CFs and the metal matrix of the metal based composites. In this study, copper was coated on the surface of continuous CFs by electroplating in acidified copper sulfate electrolyte system. The effects of electroplating parameters such as current density, plating time, plating temperature and the pH value of electrolyte solution on the electroplating of the copper thin films on CFs were studied. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to determine the microstructure of the copper coatings, and its composition and crystal structure. The thermal gravimetric analysis (TGA) was used to study the thermal stability of the CFs after electroplating. The results showed that high quality copper-coated CFs can be obtained under the optimized plating parameters as follows: the current density 3~4mA/cm2, electroplating time 10~20min, the temperature and the pH value of electrolyte solution 3.0~4.0, 20~30°C respectively. The coatings were uniform and smooth, which were adhered to CFs. XRD patterns indicated that the copper coatings were mainly composed of pure copper. And TGA results identified an increase in thermal stability of the copper coated CFs.

High Temperature Resistance of Polyborosilazane/Epoxy Resin Curing System

In this paper, Polyborosilazane (PBSZ) was successfully synthesized and used as curing agents for epoxy resin. FTIR, TGA, XRD, SEM were used to analyze the curing mechanism, curing temperature and thermal stability of the curing system. The results indicated that PBSZ could be used as curing agents for bisphenol A epoxy resin when its usage amount was 30-60 wt.% at the temperature between 100 ∼ 150 °C. Additionally, the thermal stability of PBSZ cured epoxy resin samples were better than that of epoxy resin cured with 4, 4-diaminodiphenylsulfone (DDS), showing a higher residual weight at 900°C. As PBSZ content increased, the residual weight of PBSZ cured epoxy resin at 900°C increased. When PBSZ content was 30%, the surface of cured epoxy resins was smooth without obvious defects. However, the surface became coarse when PBSZ content was further increased.

Curing Process and Heat-Resistance of Polyethersulfone Toughened Epoxy Resins

In order to improve the toughness of epoxy resin, hydroxyl-terminated polyethersulfone (PES) with various amounts (0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%) were added to bisphenol A epoxy resin (DER331)/ curing agent DETDA (E100) systems, and the influence of PES contents on curing process and heat-resistance was studied. Non-isothermal DSC was used to determine the curing process of uncured DER331/E100/PES systems at heating rate of 2°C/min, 5°C/min, 7°C/min, 10°C/min and 15°C/min separately, and the apparent activation energy was calculated based on Kissinger method. The morphology of the etched cured DER331/E100/PES systems with different PES contents was observed by SEM. The heat-resistance of these systems was investigated by DSC and TGA. The results showed that with the increasing of PES content the curing exothermic peak, the heat of curing reaction, the initial and final curing temperature all decreased at the first and then increased, indicating that when the PES content was low (5 wt.%, 10 wt.%), PES can facilitate the curing process, while, when PES content up to 15 wt.%, PES can prevent or weaken the curing reaction. SEM results indicated that the phase structure changed drastically depending on the PES content. The systems with 5 wt.% and 10 wt.% PES were epoxy-rich phase, with 15 wt.% PES was co-continuity phase, and with 20 wt.% PES showed complete phase inversion (PES rich phase). The glass transition temperature and thermo gravimetric analysis demonstrated that the addition of PES can increase the heat resistance of cured DER331/E100/PES systems.

Effect of Surface Treatment on the Mechanical Performance of PPTA-Pulp Reinforced Rubber Composites in Supercritical Carbon Dioxide Fluid

A facile surface modification method for PPTA-pulp was developed to improve the adhesion to rubber matrix. Tensile strength tests and SEM were used to evaluate the adhesion of PPTA-pulp with rubber matrix, and the results indicated that surface treatment of PPTA pulp in supercritical carbon dioxide fluid was an efficient method to increase interfacial adhesion between PPTA-pulp and rubber matrix. Attenuated Toyal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface structure and composition of untreated and treated PPTA-pulp in supercritical carbon dioxide fluid. The results indicated that the interaction of macromolecules, the crystal structure and the surface composition of PPTA-pulp changed during supercritical carbon dioxide fluid, particularly for the surface morphology and composition.

Structure and Performances of Plasticized Melt-Spun Polyacrylonitrile Precursor Fiber

The structure and performances of melt-spun PAN precursor fiber were studied by combination of SEM, DSC, UV and so on. The tensile strength of melt-spun PAN precursor fiber is 0.68GPa. The surface is very smooth and the cross-section is around. Due to the partially cyclized structure of melt-spun precursor fiber, the exothermic peak becomes broader with reducing intensity in compared with commercial fibers from solution-spun.