羧基丁腈橡胶基阻尼复合材料的相态结构及动态力学性能

研究了羧基丁腈橡胶(XNBR)/受阻酚2,2′-亚甲基双-(4-甲基-6-叔丁基苯酚) (AO-2246)复合材料的相态结构及动态力学性能,并考察了短碳纤维(SCF)的加入对复合材料动态力学性能的影响.结果表明,XNBR/AO-2246复合材料中AO-2246的质量分数存在1个临界值(40%),当AO-2246质量分数小于该临界值时,体系呈现单相形态;当AO-2246质量分数大于该临界值时,体系呈现多相形态;XNBR/AO-2246复合材料只有1个玻璃化转变峰,随着AO-2246质量分数的增加,损耗因子峰值(tan δmax)先增大后减小,玻璃化转变温度(Tg)向高温方向移动至室温;当AO-2246质量分数为50%时,tan δmax高达3.5;加入SCF后,XNBR/AO-2246复合材料的tan δmax值大幅度下降至2.5左右,但当SCF质量分数为30%时,tan δmax值升高至2.8;SCF的加入使XNBR/AO-2246复合材料的Tg略有升高,且SCF用量越大,Tg越高,同时XNBR/AO-2246复合材料的储能模量大幅度增加.     

Effects of a hindered phenol compound on the dynamic mechanical properties of chlorinated polyethylene,acrylic rubber,and their blend

The dynamic mechanical properties of binary hybrids of chlorinated polyethylene (CPE) and acrylic rubber (ACM) with 3,9‐bis{1,1‐dimethyl‐2[β‐(3‐tert‐butyl‐4‐ hydroxy‐5‐methylphenyl)propionyloxy]ethyl}‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) and their ternary hybrids were investigated. The addition of AO‐80 was successful in tailoring the damping profile. The ACM/AO‐80 hybrids show only one relaxation, which is larger than that of pure ACM, whereas for the CPE/AO‐80 hybrids, one novel relaxation appears above the glass‐transition temperature of CPE. In the case of CPE/AO‐80/ACM, a supramolecular network was formed by a crosslink due to hydrogen bonding. The replacement of a part of CPE by ACM increased the value in the middle of two peaks. The AO‐80 molecule, which is a bifunctional hydrogen‐bonding acceptor, was found to act as a compatibilizer. In addition, in such ternary hybrids, the tan δ value in the middle of the two peaks was found to be proportional to the slope of the E′ curve at an identical temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2468–2473, 2001     

Comparison of thermal techniques for glass transition measurements of polystyrene and cross-linked acrylic polyurethane films

There are few quantitative comparisons in the literature between glass transitions (T_g) measured by differential scanning calorimetry (DSC) and by dynamic mechanical analysis (DMA). Also, in the case of DMA, two different operational definitions have been used to obtain the glass transition, namely, the loss modulus (E″) and damping (tan δ) peak temperatures. We propose a new DMA definition of T_g and demonstrate that it agrees with DSC T_g measurements within ±2°C for both thermoplastic polystyrene and thermoset cross-linked acrylic polyurethane films with measurable tan δ peaks. The glass transitions for a single polystyrene standard and several cross-linked acrylic polyurethane films were measured by DSC. Additionally, E″ and tan δ peak temperatures were measured by DMA as a function of frequency and temperature. Empirically, it was determined that the average of the E″ and tan δ peak temperatures measured at 1 rad/s oscillation frequency corresponds to the glass transition measured by the ASTM E1356 DSC test method. © 1994 John Wiley & Sons, Inc.     

Effect of monomer composition on properties of copolyimides derived from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride/4,4′‐oxydianiline/1,3‐bis (4‐aminophenoxy)benzene

A series of uncontrolled molecular weight homopolyimides and copolyimides based on 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA)/4,4′‐oxydianiline (4,4′‐ODA)/1,3‐bis(4‐aminophenoxy)benzene (TPER) were synthesized. All the polyimides displayed excellent thermal stability and mechanical properties, as evidenced by dynamic thermogravimetric analysis and tensile properties testing. A singular glass transition temperature (T_g) was found for each composite from either differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA), but the values determined from tan δ of DMA were much different from those determined from DSC and storage modulus (E′) of DMA. The Fox equation was used to estimate the random T_g values. Some composites exhibited re‐crystallization after quenching from the melt; upon heating, multi‐melting behavior was observed after isothermal crystallization at different temperatures. The equilibrium melting temperature was estimated using the Hoffman‐Weeks method. Additionally, DMA was conducted to obtain E′ and tan δ. Optical properties were strongly dependent on the monomer composition as evidenced by UV‐visible spectra. X‐ray diffraction was used to interpret the crystal structure. All the results indicated that composites with TPER composition ≥ 70% were dominated by the TPER/s‐BPDA polyimide phase, and ≤40% by the 4,4′‐ODA/s‐BPDA polyimide phase. When the ratio between the two diamines was close to 1:1, the properties of the copolyimides were very irregular, which means a complicated internal structure. Copyright © 2011 Society of Chemical Industry     

Short jute fiber‐reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber‐reinforced polypropylene (PP) composites were prepared using a high‐speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999     

Effect of Hindered Phenol AO‐80 on the Damping Properties for Nitrile‐Butadiene Rubber/Phenolic Resin: Molecular Simulation and Experimental Study

A combined study of molecular dynamics (MD) simulation, experimental, and linear regression analysis method is presented for hindered phenol of 3,9‐bis[1,1‐dimethyl‐2‐{b‐(3‐tertbutyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro‐[5,5]‐undecane (AO‐80)/nitrile‐butadiene rubber/linear phenolic resin (AO‐80/NBR/PR) composites with different AO‐80 contents to quantitatively establish the relations between microstructure and damping performance. The number of hydrogen bonds (N_HBs), the fractional free volume (FFV), and the binding energy (E_binding) of AO‐80/NBR/PR composites with different AO‐80 content are calculated by MD simulation from the microscopic scale. Damping parameters, including the loss factor peak (tan δ_max) and the loss peak area (TA) (tan δ > 0.3), are obtained by dynamic mechanical analysis from macroscopic scale. The quantitative relationships between microstructure parameters (N_HBs, E_binding, and FFV) and macroscopic damping properties (tan δ_max and TA) are obtained by linear regression analysis. This research is expected to provide a theoretical guidance for improving the damping performance of rubber‐based organic hybrid composites.     

Effect of silica filler on dynamic mechanical properties of lonic elastomer based on carboxylated nitrile rubber

Variation of dynamic mechanical propeties like storage modulus (E′) and loss tangent (tan δ) with temperature show the presence of two transitions in the carboxylated nitrile rubber (XNBR) molded in the presence of zinc oxide (ZnO). The low-temperature transition is due to the glass–rubber transition (T_g) of XNBR, and the high-temperature transition is due to formation of ionic clusters. Incorporation of reinforcing silica filler makes the high temperature transition more prominent and high filler loading casues a shift of the transition temperature to the higer side. It is believed that the rubber–filler interaction in the cluster region causes striking changes in the variation of E′ and tan δ with a double-strain amplitude (DSA). © 1995 John Wiley & Sons, Inc.     

Impact of aliphatic amine comonomers on DGEBA epoxy network properties

This study characterized the mechanical and thermal properties of the oligomer‐based formulations of the diglycidyl ether of bisphenol A (DGEBA) cured with series aliphatic amines (triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and O,O bis (2‐aminopropyl propylene glycol) (Jeffamine D230) with different functionalities in the glassy state. Impact Izod and three‐point bending tests were conducted to determine the networks' impact energy (E_i), elasticity modulus (E_y), yield stress (σ_y) and fracture toughness (K_IC) values. The same three‐point bending mode was also employed to characterize the systems' thermo‐mechanical properties (DMA) and storage modulus (E') and damping modulus (tan δ = E"/E') values. The DGEBA/D230 network showed greater flexibility, maximum impact energy, higher fracture toughness, and a lower yield stress than the DGEBA/TETA and DGEBA/TEPA networks. The fracture behavior of these epoxy systems was correlated to the molecular weight between the crosslink points, M_c, and the plastic zone size (r_p) at the crack tip carved in the samples. The DGEBA/D230 network had the highest storage modulus and tan δ intensity, together with higher toughness and deformation during the network's fracture. These results were a consequence of the structural characteristics of comonomers, including their chain segment flexibility, molecular weight between crosslink points and functionality. POLYM. ENG. SCI., 54:2132–2138, 2014. © 2013 Society of Plastics Engineers     

Dynamic mechanical response of model epoxy networks in the glassy state

The dynamic mechanical properties of model epoxy-amine networks are investigated in the glassy state over a wide range of frequencies, at temperatures between 123 K and 350 K. The effects of crosslink density and network chain flexibility on the β relaxation are examined. Motions responsible for the β process begin to develop at the same temperature, whatever the crosslink density. However, an increase in crosslink density is accompanied by an increase in amplitude and a broadening towards high temperatures of both damping tan δ and loss modulus E″. This effect is responsible for the decrease of elastic modulus E′ at room temperature with increasing crosslink density.     

DMA analysis of the damping of ethylene–vinyl acetate/acrylonitrile butadiene rubber blends

The mechanical and damping properties of blends of ethylene–vinyl acetate rubber (VA content > 40% wt) (EVM)/acrylonitrile butadiene rubber (NBR), with 1.4 phr BIPB [bis (tert‐butyl peroxy isopropyl) benzene] as curing agent, were investigated by DMA and DSC. The effect of chlorinated polyvinyl chloride (CPVC), silica, carbon black, and phenolic resin (PF) as a substitute curing agent, on the damping and mechanical properties of EVM/NBR blends were studied. The results showed that 10 phr CPVC did not contribute to the damping of EVM700/NBR blends; Silica could dramatically improve the damping of EVM700/NBR blends because of the formation of bound rubber between EVM700/NBR and silica, which appeared as a shoulder tan δ peak between 20 and 70°C proved by DMA and DSC. This shoulder tan δ peak increased as the increase of the content of EVM in EVM/NBR blends. The tensile strength, modulus at 100% and tear strength of the blend with SiO₂ increased while the elongation at break and hardness decreased comparing with the blend with CB. PF, partly replacing BIPB as the curing agent, could significantly improve the damping of EVM700/NBR to have an effective damping temperature range of over 100°C and reasonable mechanical properties. Among EVM600, EVM700, and EVM800/NBR/silica blend system, EVM800/NBR/silica blend had the best damping properties. The EVM700/NBR = 80/10 blend had a better damping property than EVM700/NBR = 70/20. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and damping properties of (waste rubber powder)/hindered phenol composites

Waste rubber powder (WRP)/hindered phenol composites were successfully prepared by mixing tetrakis[methylene‐3‐(3‐5‐ditert‐butyl‐4‐hydroxy phenyl) propionyloxy] methane (AO‐60) into WRP for modification and recycling. The damping properties of the composites were systematically investigated through dynamic mechanical analysis. The experimental results indicate that the damping loss factor (tan δ) of WRP increases sharply from 0.366 to 0.734 via the modification process. With an increase in AO‐60, the tan δ value and the storage modulus in the glassy state gradually increase, and temperature dependence of loss peak gradually improves. The effects of the particle size of WRP, vulcanization temperature, vulcanization pressure, and vulcanization time on damping properties of the composite were investigated further. J. VINYL ADDIT. TECHNOL., 20:225–229, 2014. © 2014 Society of Plastics Engineers     

Damping analysis of polyurethane/polyacrylate interpenetrating polymer network composites filled with graphite particles

The graphite‐filled polyurethane/poly(methyl methacrylate‐butyl methacrylate) (PU/P(MMA‐BMA)) semi‐interpenetrating polymer networks (IPNs) were synthesized by sequential method. The influences of graphite particle content and size on the 60/40 PU/P(MMA‐BMA) IPNs were studied. The damping properties of IPN composites were evaluated by dynamic mechanical thermal analysis (DMA) and cantilever beam resonance methods. The mechanical performances were investigated using tensile and hardness devices. DMA results revealed that the incorporation of graphite particles improved damping properties of IPNs significantly. The 5% graphite‐filled IPN composite exhibited the widest temperature range and the highest loss factor (tan δ) when the test frequency was 1 Hz. As to the damping properties covering a wide frequency range from 1 to 3,000 Hz, the addition of graphite particles broadened the damping frequency range (Δf, where tan δ is above 0.3) and increased the tan δ value of IPNs. Among them, the composite with 7.5% graphite showed the best damping capacity. And the hardness and the tensile strength of IPN composites were also improved significantly. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Dynamic mechanical study on the thermal aging of a hydroxyl‐terminated polybutadiene‐based energetic composite

In an attempt to determine the aging behavior of hydroxyl‐terminated polybutadiene‐based composite solid propellants, viscoelastic measurements were used to study the effect of thermal aging on this kind of energetic material. Accelerated‐aging tests at 40, 60, and 80°C were performed for 5000 h. The changes in the dynamic mechanical properties, including the storage modulus (E′) and loss factor or damping efficiency (tan δ), with time and temperature were measured to determine the aging rate and likely mechanisms occurring during this process. An Arrhenius analysis based on the determination of relative rate constants showed a linear tendency from tan δ values, whereas a significant curvature was found from E′ values. In addition, the effects of external (surface) and internal (core) sampling in the intensification of the aging process were analyzed. The results confirmed dynamic mechanical analysis as a powerful tool for determining the aging characteristics of composite propellants. This technique allows the evaluation of the actual state of a propellant grain with a small sample and a straightforward measurement. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2397–2405, 2003     

Dynamic mechanical properties of conductive carbon black‐reinforced closed cell microcellular oil‐extended EPDM rubber vulcanizates: Effect of blowing agent,temperature, frequency,and strain

Dynamic viscoelastic properties of Vulcan XC 72 (excess conductive carbon black)‐reinforced solid‐ and closed‐cell microcellular controlled long chain branching grade oil‐extended EPDM (Keltan 7341A) rubber vulcanizates were studied at four frequencies of 3.5, 11, 35, and 110 Hz, and at a temperature range of ?100 to 160°C.The effect of blowing agent (ADC 21) loading on storage modulus (E′) and loss tangent (tan δ) was studied. The log of storage modulus bears a linear relationship with the log of density for both solid and microcellular rubber. Relative storage modulus (E/E) decreases with decrease in relative density (ρ_f/ρ_s). Both E′ and tan δ were found to be dependent on frequency and temperature. The master curves of the storage modulus versus log temperature‐reduced frequency were formed by superimposing E′ results and by using shift factors calculated by Arrhenius equation. Strain‐dependent isothermal dynamic viscoelastic properties were carried out for dynamic strain amplitude of 0.08–7%. Cole–Cole plots of microcellular vulcanizates show a circular arc with blowing agent (density). Empirical relationship between tan δ versus E′ is found to be linear, whose slope is independent of blowing agent loading or density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1600–1608, 2006     

Structure and dynamic properties of nitrile‐butadiene rubber/hindered phenol composites

Crosslinked nitrile‐butadiene rubber (NBR)/hindered phenol composites were successfully prepared by mixing tetrakis [methylene‐3‐(3‐5‐ditert‐butyl‐4‐hydroxy phenyl) propionyloxy] methane (AO‐60) into NBR with 35% acrylonitrile mass fraction. The structural and mechanical properties of the NBR/AO‐60 composites were systematically investigated by using differential scanning calorimeter, XRD, Fourier transform infrared, scanning electronic microscope, dynamic mechanical analyzer, and tensile testing. The results indicated that the AO‐60 changed from crystalline form into amorphous form, and most of the AO‐60 molecules could be uniformly dispersed in the NBR matrix. The glass transition temperature (T_g) of NBR/AO‐60 composites increased gradually with increasing content of AO‐60. The increase in T_g could be attributed to the formation of a strong hydrogen bonding network between the AO‐60 molecules and the NBR matrix. Unlike the pure NBR, the NBR/AO‐60 rubber composites had only one transition with a high loss factor. With increasing content of AO‐60, the loss peak shifted to the high temperature region, the loss factor increased from 1.45 to 1.91, and the area under the tan δ versus temperature curve (TA) also showed a significant increase. All these results were ascribed to the good compatibility and strong intermolecular interactions between NBR and AO‐60. Furthermore, all NBR/AO‐60 composites exhibited higher glass transition temperatures and tensile strength than NBR, and they had other desirable mechanical properties. They have excellent prospects in damping material applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Transition magnitudes and impact improvement in rubber-modified plastics

Impact strength at room temperature and dynamic mechanical properties over a temperature range have been studied for a number of rubber reinforced glassy state plastics. The rubber phases in every case were butadiene copolymers of known composition and particle size and selected for their good dispersion after blending into the various matrices. This dispersion was checked by electron microscopy and the in situ particle size evaluated. The matrices were based on homo- and co-polymers of styrene, methyl methacrylate and acrylonitrile. A vibrating reed apparatus was employed to measure the storage component of Young's modulus (E′) and loss factor (tan δ) at essentially constant frequency (～300 Hz) through the rubber relaxation region. The Izod impact strength was measured in accordance with the standard method ASTM D-256. A gross parallel was found between impact strength and transition magnitude as measured by the change in modulus between ?100°C and 20°C (ΔE′) or the tan δ peak area with, for example, increasing volume fraction of rubber phase. However, when the same rubber was dispersed in different matrices a more subtle effect was an inverse proportionality of tan δ area with E′ measured at the peak temperature. Conversely ΔE′ after correction for matrix modulus change was shown both theoretically and experimentally to be directly proportional to E′ of the matrix at room temperature. The impact strength actually increases with ΔE′ and not with tan δ area in these cases. However, a more important requirement for good impact is compatibility between the rubber and matrix, but neither ΔE′ nor tan δ reflect this. After correction of tan δ areas to constant matrix modulus there remains an increase of area with particle size. Impact strength also increases strongly with particle size for compatible systems. The applicability of Hashin's central equation and Mackenzie's equation in describing the systems is discussed.     

Morphology and dynamic mechanical properties of natural rubber/nitrile rubber blends containing trans‐polyoctylene rubber as a compatibilizer

The use of trans‐polyoctylene rubber (TOR) as a compatibilizer for blends of natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated using atomic force microscopy (AFM) and dynamic mechanical analysis (DMA). The NR/NBR blends containing varying proportions of TOR were prepared in an internal mixer. AFM micrographs of NR/NBR blend at 50/50 (w/w) composition showed heterogeneous phase morphology with NR as a matrix and NBR as a dispersed phase. Inclusion of TOR in the NR/NBR blend altered the phase morphology by reducing the size of the NBR phase. DMA of NR/NBR/TOR showed reduction in tan δ peak height of NBR and an increase in storage modulus E′ in the rubbery region for the NR/NBR blends. A comparison of the E′ obtained from experimental data with that from theoretical models was made to deduce the location of TOR in the blend. Based on the fittings of calculated and experimental values of E′, it was inferred that TOR was incorporated into the NR phase at lower proportion as well as at the interfacial region at higher proportion. The Cole–Cole plot illustrated the compatibilizing effect of TOR. Copyright © 2004 Society of Chemical Industry     

Dynamic mechanical properties in blends of poly(styrene‐b‐isoprene‐b‐styrene) with aromatic hydrocarbon resin

The damping properties in blends of poly(styrene‐b‐isoprene‐b‐styrene) (SIS) and hydrogenated aromatic hydrocarbon (C₉) resin were investigated by dynamic mechanical analysis. SIS exhibited two independent peaks of loss factor (tan δ) corresponding to the glass transition of polyisoprene (PI) and polystyrene (PS) segments, respectively. The addition of hydrogenated C₉ resin had a positive impact on the damping of SIS. With the increasing softening point and content of the resin, the main tan δ peak shifted to higher temperatures and the useful damping temperature range was broadened. Addition of mica or PS was found to widen the effective damping range evidently in the high‐temperature region, especially when PS was mixed in the solid state. It was concluded that the dispersed PS domains played a role of reinforcing fillers at low temperatures and served as a polymer component with a tan δ peak due to its glass transition at the high temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4157–4164, 2006     

Effect of hydrogen bond formation on dynamic mechanical properties of amorphous cellulose

The temperature dependence of the dynamic modulus (E′) and the mechanical loss tangent (tanδ) of amorphous cellulose prepared from cellulose triacetate by saponification was measured and compared with that of cellophane, recrystallized cellulose obtained by immersing amorphous cellulose in water, and cellulose triacetate. The E′ of amorphous cellulose decreased initially with increasing temperature and then began to increase at about 70°C with a maximum at 80°C, decreasing again at about 100°C. Another decrease in E′ was observed at 220°C accompanied by a discontinuity at 155°C. In the tan δ-versus-temperature curve, a medium peak at 60°C a shoulder peak at 146°C, and a broad peak at 200°C were observed. It was found that the transition at about 60°C was related to hydrogen bond formation by free OH groups. The transition at about 150°C was attributed to a recrystallization process by heating, and the relaxation at 200°C, to the glass transition of the polymer. The decrement in E′ observed at about 100°C was attributed to the cooperative motion of an individual pyranose ring in amorphous cellulose, juding from the E′ and tan δ assignment of other cellulose materials. The change in E′ was also measured isothermally as a function of time in the temperature range between 40°C and 80°C, where a maximum in tan δ and an increment in E′ were observed as the temperature dependence of the dynamic viscoelasticity. The change in E′ with elapsed time was analyzed kinetically, and an activation energy of 2.6 kcal/mole was calculated. This value is the expected activation energy of hydrogen bond formation.     

Dynamic moduli for short fiber-CR composites

The dynamic moduli, E′ and E″, and tan δ for nylon–CR and PET–CR composites with unidirectional short fibers were studied as a function of temperature by using a Rheovibron. The temperature dependence of tan δ showed two dispersion peaks for nylon–CR composite. The peak at ?28°C corresponded to the main dispersion of CR and the peak at 100°C to the α-dispersion of nylon 6. For a PET-CR composite, in addition to the individual dispersion of CR and PET, a small and broad peak was observed at about 90°C. The angular dependence of E′ indicated that the short fibers assumed good orientation. The storage modulus for the composites was given by the parallel model as E′ = V_f′E_f + V_mE′_m., where E′_c, E′_f and E′_m were the storage modulus for the composite, fiber, and matrix and V_f and V_m were the volume fraction of fiber and matrix, respectively. In the transverse direction of fiber, the peak values of tan δ at ?28°C were given by the following equation; tan δ_c = tan δ_m ? δV_f, where tan δ_c and tan δ_m are the loss tangent for the composite and matrix, respectively, and α is coefficient depending on fiber type. The results indicated that a region with strong interaction was formed between fibers and CR matrix.