Influence of structure of amines on the properties of amines‐modified reduced graphene oxide/polyimide composites

Graphene oxide (GO), as an important precursor of graphene, was functionalized using alkyl‐amines with different structure and then reduced to prepare reduced amines grafted graphene oxide (RAGOs) by N₂H₄ · H₂O. The successful chemical amidation reaction between amine groups of alkyl‐amines and carboxyl groups of GO was confirmed by Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA). Then RAGOs/polyimide nanocomposites were prepared via in situ polymerization and thermal curing process with different loadings of RAGOs. The modification of amine chains lead to homogenous dispersion of RAGOs in the composites and it formed strong interfacial adhesion between RAGOs and the polymer matrix. The mechanical and electrical properties of polyimide (PI) were significantly improved by incorporation of a small amount of RAGOs, the influence of structure of amines grafted on RAGOs on the enhancement effects of composites was discussed. The research results indicated that the proper structure of amine could effectively enhance the properties of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43820.     

Dynamic mechanical properties of N-phenylnadimide modified PMR polyimide composites

Temperature-frequency dependence of α, β, and γ transitions was determined using a Rheometrics dynamic spectrometer on a series of unidirectional Celion 6000/N-phenylnadimide (PN) modified PMR polyimide composites. The objective was to see if any correlations exist between crosslinked network structure and dynamic mechanical properties. Variation in crosslinked network structures was achieved by altering the polyimide formulation through addition of various quantities of PN into the standard PMR-15 composition. As a control, PMR-15 composite system exhibited well-defined α, β, and γ transitions in the regions of 360, 100, and −120°C, respectively. Their activation energies were estimated to be 232, 60, and 14 kcal/mole, respectively. Increasing the amount of PN concentration caused (a) lowering of the activation energies of the three relaxations, (b) a decrease of the glass transition temperature, and (c) increasing intensities of the three damping peaks, compared to the control PMR-15 counterpart. These dynamic mechanical responses were in agreement with formation of a more flexible co-polymer from PN and PMR-15 prepolymer.     

Thermal and mechanical properties of blended polyimide and amine‐functionalized poly(orthosiloxane) composites

Nanocomposite films were prepared through the blending of polyimide (PI) with octaphenyl silsesquioxane (OPS) and an amino‐functionalized analogue, octaaminophenyl silsesquioxane (OAPS), with a solution‐casting method. Although the PI–OPS composites showed visible phase separation at 5 wt %, the PI–OAPS composites were transparent with visible phase separation occurring only at 50 wt % OAPS. The interfacial interactions and homogeneity of the composites were characterized with scanning electron microscopy (SEM) and dynamic mechanical analysis. SEM analysis showed a uniform fracture surface for OAPS composites at concentrations up to 20 wt %. Interestingly, OAPS‐rich particles with sizes of less than 1 μm were formed within the PI matrix for the 50 wt % composite. The PI–OAPS composites showed higher glass‐transition temperatures (T_g's) than the pure PI. The PI–OPS composites showed a T_g lower than that of the pure PI, and this suggested poor interfacial interactions. The slightly enhanced thermal stability of PI–OAPS composites (up to 20 wt %) was attributed to the inherent thermal stability of OAPS at higher temperatures. There were small increases in the modulus and strength for the composites with respect to the base polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Processing and properties of new high-temperature,lightweight composites based on foam polyimide binder

We report a method for making novel, lightweight (ρ = 0.3–1.1 kg/dm³) polymer composites based on high-temperature foam polyimide binder, carbon fibers, and organic fibers. The density and mechanical properties of the foam composite can be varied over a relatively wide range, depending on the volume contents of the fiber and air pores. The resin's high glass transition temperature of 260°C, coupled with the high thermal stability of carbon or polyimide fibers, contributes to its excellent retention of mechanical properties at elevated temperatures. The temperature at the beginning of weight loss is not lower than 570°C and depends on the kind of fiber felt. The combination of excellent thermal and specific mechanical properties of foam composites together with exceptional thermal stability and processability on conventional molding equipment can provide unusual performance for the new design of advanced materials and structures.     

Influence of grafted polypropylene on the mechanical properties of mineral‐filled polypropylene composites

The purpose of this work was to study how mineral fillers would behave in a polypropylene (PP) matrix when PP modified with maleic anhydride (MA) and/or itaconic acid (IA) was used as a coupling agent in the preparation of mineral‐filled PP composites. The composites were characterized with tensile mechanical measurements and morphological analysis. The optimum amount of the coupling agent to be used to obtain composites with improved mechanical properties was established. The results indicated that these coupling agents enhanced the tensile strength of the composites significantly, and the extent of the coupling effect depended on the nature of the interface that formed. The incorporation of coupling agents enhanced the resistance to deformation of the composite. The behavior of IA‐modified PP as a coupling agent was similar to that of a commercial MA‐modified PP for the filled PP composites. Evidence of improved interfacial bonding was revealed by scanning electron microscopy studies, which examined the surfaces of fractured tensile test specimens; their microstructures confirmed the mechanical results with respect to the observed homogeneous or optimized dispersion of the mineral‐filler phase in these composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2343–2350, 2007     

Microstructure,mechanical properties,and flame retardancy of nanoclay‐incorporated polyurethane flexible foam composites

The present work seeks to investigate microstructure, mechanical properties, and flame retardancy of polyurethane/nanoclay flexible foam composites. In this regard, we prepared various nanocomposites with and without nanoclay and observed the resulting morphologies to correlate them with the other corresponding characteristics. The results provided support for the fact that tensile strength and compression set will increase with nanoclay content, while elongation at break and tear strength decrease to some extent. Flame‐retardancy test results showed that the introduction of nanoclay into the polyurethane flexible foam causes an almost optimal trend in the flame retardancy over clay content. The microcellular‐properties correlations were established on account of changes in microcell architecture. J. VINYL ADDIT. TECHNOL., 22:415–422, 2016. © 2015 Society of Plastics Engineers     

Electro conductivities of well‐dispersed PMMA‐g‐MWNTs/6FDA‐based polyimide composites: Effect of chemical structure

PMMA (polymethylmethacrylate), which is miscible with hexafluoropropane dianhydride (6FDA)‐based polyimide, was grafted onto MWNTs surfaces to enhance their dispersion relative to that of pristine MWNTs. The electrical conductivity of the 6FDA‐based composite revealed percolation threshold behavior, and the 6FDA‐4,4′‐(hexafluoroisopropylidene)diamine, (6FpDA):3,5‐diaminobenzoic acid (DABA)/PMMA‐g‐MWNT composite showed a higher percolation threshold concentration and a slightly lower critical exponent compared with those of the 6FDA‐6FpDA composite. Because of the weak interaction energies between 6FDA‐6FpDA:DABA and PMMA, agglomerated domains were formed. Also, the weak interaction energies of the 6FDA‐6FpDA:DABA led to a larger reduction in the normalized transmittance compared with that seen in the 6FDA‐6FpDA composite. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Preparation and properties of APPSSQ‐like/polyimide hybrid composites

Hydrolysis and condensation proceeded to generate 3‐aminopropyl polysilsesquioxane‐like (APPSSQ‐like) particles from 3‐aminopropyl triethoxysilane. An APPSSQ‐like particle includes two domains: crosslinking Si? O? Si networks inside and 3‐aminopropyl groups outside the particle. The APPSSQ‐like/polyimide (APPSSQ‐like/PI) hybrid composites were prepared from a solution of poly(amic acid) (PAA, polyimide precursor) and APPSSQ‐like particles using N,N‐dimethylacetamide as a solvent. Scanning electron microscopy (SEM) showed that the APPSSQ particle sizes were about 100 nm, and there was no obvious phase separation between the APPSSQ‐like particles and the PI matrix in the fracture surfaces of the hybrid films. Owing to the highly crosslinked Si? O? Si networks inside the APPSSQ‐like particles, the APPSSQ‐like/PI hybrid composites possessed desired properties such as improved thermal resistance and reduced coefficients of thermal expansion (CTE). The presence of covalent bonds between the APPSSQ‐like particles and the PI molecules improved the compatibility between these two components. Thus, the tensile strength increased with the APPSSQ‐like content, and the elongation at break also slightly increased with the APPSSQ‐like content. The initial tensile and storage moduli of the APPSSQ‐like/PI hybrid composites increased with the APPSSQ‐like content, which indicates that the mechanical properties of these hybrid composites were enhanced by the incorporation of the APPSSQ‐like content in the PI matrix. Furthermore, the glass transition temperatures of these composites increased with the APPSSQ‐like content because the adhesion between the APPSSQ‐like particles and the PI molecules restricts the PI chains' mobility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2865–2874, 2003     

Effect of HTPB structure on prepolymer characteristics and on mechanical properties of polybutadiene-based polyurethanes

Oligobutadiene-based prepolymers and polyurethanes (PU) were prepared from hydroxyl terminated polybutadiene (HTPB), three diisocyanates (aromatic, alicyclic and aliphatic) and two chain extenders (containing hydroxyl or amino groups). The free NCO content in the prepolymers varied systematically and the characteristic of these products were interpreted in terms of NCO group reactivity, propagation reactions and HTPB functionality. The mechanical properties of the polyurethane elastomers derived from the prepolymers were discussed in terms of hard and soft segment structures.     

Effects of reactive end-capper on mechanical properties of chemical amplified photosensitive polyimide

Photosensitive polyimide (PSPI) was synthesized and characterized to replace the conventional polyimide buffer layer because direct patterning with PSPI could reduce the processing procedure to the half. Since PSPI should be dissolved in alkaline aqueous solution and have good mechanical properties after imidization, low molecular weight of PSPI was synthesized with reactive end-capper, which could extend the chain length of PSPI during imidization. Therefore norbornene end-capped PSPI precursor was synthesized with various 5-norbornene-2,3-dicarboxylic anhydride (NDA) content.Although molecular weight of PSPI decrease with increasing NDA content, the elongation at break and the glass transition temperature (T_g) of PSPI films imidized at 300 °C increased with increasing NDA content. On the other hand, elongation at break of PSPI films imidized at 350 °C decreased but T_g of those increased with increasing NDA content. Above T_g, thermal expansion coefficient decreased dramatically by introducing NDA end-capper. From mechanical and thermal properties of PSPI, it appears that low molecular weight of PSPI can be chain-extended and crosslinked during imidization.     

Preparation and properties of a novel flame retardant polyurethane quasi‐prepolymer for toughening phenolic foam

A novel phosphorus‐ and nitrogen‐containing polyurethane quasi‐prepolymer (PNPUQP) was synthesized and incorporated into phenolic foam (PF) in different ratios in order to improve the toughness. The structure of PNPUQP was confirmed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR). The effects of PNPUQP on the flame retardant properties, thermal stability and mechanical properties of modified PF were investigated. The results suggested that the addition of 3 wt % PNPUQP increased the toughness of PF and improved the flame retardancy. The investigation on the morphology of PF and modified PF by scanning electron microscope (SEM) certified the good toughness of the PNPUQP on PF. Additionally, the thermal properties of the foams were investigated by thermogravimetric analysis (TGA) under N₂ atmosphere. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42424.     

纳米填料对聚氨酯泡沫弹性体力学性质影响的研究

在传统的聚氨酯(PU)泡沫塑料制法的基础上，为了改善聚氨酯泡沫塑料的性能，根据各个不同的配方添加不同量的纳米二氧化硅(SiO2)填料。并依此再调节各种辅助剂的用量。分别制得纳米材料增强软质聚氨酯泡沫塑料弹性体。实验结果表明，加入的纳米填料和PU材料有很好的相容性。可以均匀地分布在PU材料之中，使PU泡沫的压缩永久变形大幅度下降。     

硅氧烷预聚体改性热塑性酚醛树脂的交联结构及其力学性能

通过不同预聚程度的环氧化硅氧烷（ES）与酚醛树脂共固化及固化物理状态的调控,构建不同拓扑结构的交联网络,探讨了不同预聚程度的硅氧烷预聚体（PES）改性热塑性酚醛树脂（NR-PES）交联网络的调控及其强韧化的构建方法。首先,合成了一种不同预聚程度的环氧化硅氧烷（PES）,通过DSC和流变分析,明确了NR-PES的固化反应和物理状态特征,在此基础上,确定了不同交联结构NR-PES的制备方法。接着,采用DMA、TGA、力学测试研究了PES的预聚程度对NR-PES交联网络和性能的影响规律。结果表明,当PES预聚程度较低时,NR-PES的交联密度较低,导致其热稳定性和弯曲强度较低;随着PES预聚程度的增加,NR-PES的交联密度不断增加,其热稳定性、弯曲强度随之增加,但K_IC不断降低。特别是,PES的预聚程度为30%时,2-NR-PES展现出优异的热稳定性、弯曲强度和断裂韧性,残炭率C_800℃为53.43%,弯曲强度为20.51 MPa,K_IC为0.389 MPa·m^1/2。此外,当PES预聚程度过高时,NR-PES的热稳定性、弯曲强度和断裂韧性显著降低。     

Ignition and combustion of low‐density polyimide foam

The ignition, flaming and smoldering combustion of low‐density polyimide foam have been studied using a cone calorimeter. Low‐density polyimide foam exhibits a high ignition resistance. The minimum heat flux for the ignition of flaming combustion ranges from 48 to 54 kW/m². This minimum heat flux also indicates the heat flux for transition from smoldering to flaming combustion. The flaming combustion results show that the heat release rate of low‐density polyimide foam is very low even at a high incident heat flux of 75 kW/m². The smoldering combustion results show that the smoldering of low‐density polyimide foam becomes significant when the incident heat flux is greater than 30 kW/m². The smoldering combustion of low‐density polyimide foam cannot be self‐sustaining when the external heat source is removed. Copyright © 2003 John Wiley & Sons, Ltd.     

The mechanical properties of insert‐molded bimaterial composites

Bimaterial composite samples were constructed by injecting various polymers into a mold containing a fraction of a pre‐molded specimen. The resulting series composites were tested in tension. Breaking stresses were independent of fractional length. Conversely, both elongation to break and apparent stiffness varied with Although samples broke at or near the interface, adhesion was reasonably good, as indicated by transfer of material across interfaces.     

Dynamic mechanical properties of particle‐reinforced EPDM composites

The dynamic mechanical property of particle‐reinforced ethylene–propylene–diene monomer (EPDM) matrix composites has been studied by using a dynamic mechanical thermal analyzer (DMTA). The individual composite has been reinforced with the various reinforcing particles as follows: silicon carbide particles (SiCps) of 60 μm in average diameter with various volume fractions (i.e., 10–40%); copper (Cu) and aluminum (Al) particles with 20 vol %; and SiCps with 6 and 36 μm in different average diameters with 20 vol % over the total composite volume. It is shown from the experimental results that the dynamic elastic modulus values increase and the composites with 40 vol % SiCps exhibit higher tan δ values through the entire rubbery phase after the glass transition region compared with the composites with lower particle volume percentages. This shows that the composites with 20 vol % Cu particles have the higher dynamic elastic modulus but the lower peak tan δ value than the composites with other particles of 20 vol % do. Scanning electron microscopy results show that the effective particle volume in the composite with Cu particles is higher than the other composites, although the same particle volume fraction of 20% has been used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1595–1601, 2003     

Structural and mechanical properties of YBCO‐polystyrene composites

Microcrystalline powders of yttrium barium copper oxide [YBa₂Cu₃O₇] have been prepared by conventional ceramic preparation technique. The powder belong to orthorhombic symmetry with unit cell dimensions ‘a’=3.8214 Å, ‘b’=3.8877 Å and ‘c’=11.693 Å. XRD and SEM studies revealed that its particle size is in the micrometer range. Micro composites of polystyrene with different loading of yttrium barium copper oxide fillers were prepared by melt mixing in a brabender plasticorder at a rotor speed of 60 rpm. The lattice parameters of the constituent phases are the same in all the composites. Mechanical properties such as stress–strain behavior, Young's modulus, and tensile strength were studied as a function of filler loading. Addition of filler enhances the Young's modulus of the polymer. Because of the poor filler‐matrix adhesion, tensile strength and strain at break decreases with filler loading. To explore more carefully the degree of interfacial adhesion between the two phases, the results were analyzed by using models featuring an adhesion parameter. Finally experimental results were compared with theoretical predictions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and thermal properties of phenolic/glass fiber foam modified with phosphorus‐containing polyurethane prepolymer

Phenolic foam exhibits outstanding flame, smoke and toxicity properties, good insulation properties and low production costs. However, the brittleness and pulverization of phenolic foam have severely limited its application in many fields. In this study, a novel phosphorus‐containing polyurethane prepolymer (DOPU) modifier was firstly synthesized, and then the foaming formula and processing of toughening phenolic foam modified with DOPU and glass fiber were explored. The structure and reactive behavior of prepolymer and phenolic resin were investigated using Fourier transform infrared spectroscopy. The effects of DOPU and glass fiber on the apparent density, compressive strength, bending strength and water absorption were investigated. The results suggested that the apparent density, compressive strength and bending strength of modified phenolic foam tended to increase irregularly with increasing content of DOPU. The addition of DOPU led to lower water absorption of glass fiber‐filled foam. Thermal stability and flame retardancy were examined using thermogravimetric analysis and limiting oxygen index (LOI) tests. It was found that foam with 3% DOPU and 0.5% glass fiber added exhibited good thermal stability and high char yields. The LOI value of modified phenolic foams decreased with increasing DOPU content, but it still remained at 41.0% even if the amount of modifier loaded was 10 wt%. © 2012 Society of Chemical Industry     

Influence of chemical structure of hardener on mechanical and adhesive properties of epoxy polymers

The mechanical and adhesive properties of epoxy formulations based on diglycidyl ether of bisphenol A cured with various aliphatic amines were evaluated in the glass state. Impact and uniaxial compression tests were used to determine the impact energy, elastic modulus and yield stress, respectively. The adhesion tests were carried out in steel–steel joints using single‐lap shear, T‐peel, and impact adhesive joints geometry. The better mechanical and adhesive behavior of the networks is obtained when exists high flexibility of chain between crosslink and/or high elastic modulus. The 1‐(2‐aminoethyl)piperazine epoxy network presents the best adhesive properties, high flexibility, and the largest impact energy. However, it possesses low elastic modulus and yield stress. Also, exhibits increases in peel strength and impact energy while reductions in lap shear strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

硅氧烷预聚体改性热塑性酚醛树脂的交联结构及其力学性能

通过不同预聚程度的环氧化硅氧烷（ES）与酚醛树脂共固化及固化物理状态的调控,构建不同拓扑结构的交联网络,探讨了不同预聚程度的硅氧烷预聚体（PES）改性热塑性酚醛树脂（NR-PES）交联网络的调控及其强韧化的构建方法。首先,合成了一种不同预聚程度的环氧化硅氧烷（PES）,通过DSC和流变分析,明确了NR-PES的固化反应和物理状态特征,在此基础上,确定了不同交联结构NR-PES的制备方法。接着,采用DMA、TGA、力学测试研究了PES的预聚程度对NR-PES交联网络和性能的影响规律。结果表明,当PES预聚程度较低时,NR-PES的交联密度较低,导致其热稳定性和弯曲强度较低;随着PES预聚程度的增加,NR-PES的交联密度不断增加,其热稳定性、弯曲强度随之增加,但K_IC不断降低。特别是,PES的预聚程度为30%时,2-NR-PES展现出优异的热稳定性、弯曲强度和断裂韧性,残炭率C_800℃为53.43%,弯曲强度为20.51 MPa,K_IC为0.389 MPa·m^1/2。此外,当PES预聚程度过高时,NR-PES的热稳定性、弯曲强度和断裂韧性显著降低。