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Xie J.,Donghua University | Xie J.,Guangzhou Fiber Product Testing Institute | Yao L.,Donghua University | Xu F.,Donghua University | And 4 more authors.
Composites Part B: Engineering | Year: 2014

A PMR polyimide composite reinforced with three-dimensional (3D) woven basalt fabric is fabricated for medium high temperature applications. The PMR polyimide matrix resin is derived from 4,4′-methylenediamine (MDA), diethyl ester of 3,3′,4,4′-oxydiphthalic (ODPE) and monoethyl ester of Cis-5-norbornene-endo-2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin are investigated. Based on the curing reaction of the PMR type polyimide and the rheological properties, an optimum two-step fabrication method is proposed. The three dimensional fabric preforms are impregnated with the polyimide resin in a vacuum oven at 70 °C for 1 h followed by removing the solvent and pre-imidization. The composites are then consolidated by an optimized molding procedure. Scanning electron microscopy analysis shows that needle shaped voids are generated in yarns and the void volume fraction is 4.27%. The decomposition temperature and the temperature at 5% weight loss of the composite post-cured at 320 °C for 24 h are 440 °C and 577 °C, respectively. The dielectric constant and the dielectric loss of the composite are measured by circular cavity method at 7-12 GHz. The tensile strength and the modulus in the warp direction of the composite are 436 MPa and 22.7 GPa. The composite shows a layer-by-layer fracture mode in three-point bending test. The flexure strength and modulus in the warp direction of the composite are 673 MPa and 27.1 GPa, respectively. © 2014 Elsevier Ltd. All rights reserved.

Li Y.,Key Laboratory of Textile Science and Technology | Li Y.,Donghua University | Moyo S.,Key Laboratory of Textile Science and Technology | Moyo S.,Donghua University | And 4 more authors.
Industrial Crops and Products | Year: 2013

When cellulose fibers are ethanol pretreated followed by plasma treatment, their surfaces become more hydrophobic, resulting in better interfacial adhesion to hydrophobic thermoplastics. How much the improvement of composite mechanical properties could be achieved using this method is still unknown. In this study, ramie fabrics are ethanol-pretreated followed by an atmospheric helium plasma treatment for 15. s, 30. s and 45. s, respectively, in order to reveal the degree of improvement in mechanical properties of ramie-fabric-reinforced polypropylene composites. Scanning electron microscopy shows that the fiber surfaces of the treated groups become rougher and are covered with PP resin after interlaminar shear strength (ILSS) tests. X-ray photoelectron spectroscopy shows that the 30. s treated group has a 50% reduction in atomic ratio of oxygen to carbon. Water contact angle measurement demonstrates that the wettability of the surfaces of the treated fibers significantly decreases. The mechanical tests show increases of up to 39, 28 and 20% in ILSS, flexural strength and tensile strength of the treated composites compared to the control group, respectively, which may be attributed to the combined effects of the increased surface hydrophobicity due to the reaction of ethanol molecules to cellulose in plasma treatments and the roughened surface from plasma etching. © 2013 Elsevier B.V.

Zhou N.,Key Laboratory of Textile Science and Technology | Zhou N.,Donghua University | Yao L.,Key Laboratory of Textile Science and Technology | Yao L.,Donghua University | And 9 more authors.
Industrial Crops and Products | Year: 2013

Ramie/poly (lactic acid) (PLA) laminated composites were fabricated by the compression molding. To improve the mechanical properties of this type of composites, a cyclic load pre-treatment was performed. Ramie plain woven fabrics as the reinforcing material were pre-treated under wet state by cyclic tensile loading several times. The results showed that the fabrics treated by 70% level of the mean fracture load of the untreated ones with 10 cycles had the largest improvement of 38% in tensile strength. As to the mechanical properties of ramie/PLA laminated composites, the treated fabric reinforced composites had 35% higher tensile strength, 32% higher Young's modulus, 20% higher flexural strength and 17% higher flexural modulus than the untreated ones. The X-ray diffraction diagrams indicated that there was no distinct difference in crystallinity and crystalline orientation. The improvement of fabric mechanical properties is likely resulted from the increased orientation of molecules in the fibers and that of the fibers in the yarns. © 2012 Elsevier B.V.

Gao T.,Donghua University | Zhao Y.,Donghua University | Zhou G.,CAS Shanghai Institute of Ceramics | Han Y.,Donghua University | And 5 more authors.
Composites Part B: Engineering | Year: 2015

Abstract Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO2 CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO2 CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO2 and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO2 CMC was 96.9 kJ/m2, almost 4 times as much as those for typical other carbon fiber reinforced CMCs. © 2015 Elsevier Ltd. All rights reserved.

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