环氧树脂/反应性聚碳酸酯/叔胺体系的表面结构与性能

环氧树脂/反应性聚碳酸酯/叔胺体系的表面结构与性能;环氧树脂; 胺化聚碳酸酯; 形态结构     

Aging and cold crystallization of melt‐extruded poly(trimethylene terephthalate) films

We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001     

反应性聚碳酸酯/环氧树脂体系的玻璃化转变行为及力学性能

增韧;反应性聚碳酸酯/环氧树脂体系的玻璃化转变行为及力学性能     

Monitoring the glass transition temperature of polymeric composites with carbon nanotube buckypaper sensor

Carbon nanotube (CNT) Buckypapers can be infused with resin and easily incorporated into conventional fiber reinforced composites. In this paper, we propose to use Buckypaper (BP) as a new measuring method to determine the glass transition temperature of polymeric composites. The CNT-only BP was fabricated by spray-vacuum filtration method with monodispersion of multi-wall carbon nanotubes, and then co-cured with polymeric composites. After manufacturing, the glass transition temperature of polymeric composites could be obtained from the relationship between resistance and temperature of BP during the dynamic heating process. Experimental results show that the glass transition temperature of composite samples A and B monitored by BP sensors were 127 °C and 180 °C, while such temperatures obtained from a dynamical mechanical analyzer (DMA) were 128 °C and 184 °C respectively. This paper not only reveals the ability of BP as a sensor for monitoring the glass transition temperature of composite but also provides a new way to understand the glass transition phenomenon of composite.     

Temperature dependent nano indentation of thin polymer films with the scanning force microscope

The scanning force microscope (SFM) was used to investigate the temperature dependent micro mechanical properties of polymethylmethacrylate (PMMA) films with a thickness of 35 nm in the range of the radius of gyration. Force-distance curves were performed in the glass transition range to create permanent nanometric indentations with maximal forces up to 4 μN. Quantitative measurements of the indentation depth during and after application of the force, hysteresis energy and slope of the loading part are carried out as function of sample temperature and applied force. The glass transition of the polymer film can be clearly identified by the change of the mechanical properties of the polymer. Surprisingly, only a small change of elasticity at the glass transition is observed.     

Time‐Temperature Independence of Aging‐Induced Relaxation Peak in the Glassy State

Cooling a polymer glass through the glass transition temperature and then holding the material temporarily at an aging temperature produces a localized relaxation peak on its dynamic mechanical spectra. Clear evidence is provided that the aging‐induced structural relaxation is frequency‐temperature insensitive. The aging‐associated retardation time, if there is any, should therefore not relate to an activation process over temperature barriers or originate from a manipulation of the retardation spectra of the glass and the β‐transition.     

Dynamic Mechanical Behavior and Prediction for PP/POE Blends

Polypropylene(PP)/ethylene-octene copolymer(POE) blends were prepared with a twin-screw extruder.Their dynamic mechanical behavior were systematically investigated.The results show that PP/POE blends are heterogeneities with a partial compatible two-phase structure,the glass transition temperature of PP phases in the blends tends to shift towards high temperature with increasing the POE content,and the glass transition temperature of POE phases shifts towards the low temperature with increasing the PP conte...     

Mechanical properties of dual-phase polymer electrolytes prepared from poly(styrene-co-butadiene) rubber/poly(acrylonitrile-co-butadiene) rubber mixed latices

Mechanical properties of two dual-phase polymer electrolytes (DPEs), prepared from poly(styrene-co-butadiene) rubber (SBR) and poly(acrylonitrile-co-butadiene) rubber (NBR) latices, are studied. Both DPEs are composed of an SBR supporting phase and an ionconductive phase of NBR/lithium salt solution. The first DPE maintains a tensile strength of 0.5 MPa and elongation of 280% with an ionic conductivity of 10^?3 S/cm. Although the glass transition relaxations based on the dual-phase structure are not resolved in this DPE because of the proximity of the glass transition temperatures of the SBR and NBR, the glass transition shifts to a lower temperature due to the plasticization by the lithium salt solution. In the second DPE, two distinctive glass transition relaxations, corresponding to the SBR and NBR phases, are observed in the viscoelasticity versus temperature measurement, indicating the dual-phase structure. A simple equivalent mechanical model, which is modified from the Takayanagi model, is introduced to elucidate the mechanical behavior of the dual-phase structure in the second DPE. According to this model, 8% of DPE is a mechanically continuous SBR phase in the tensile direction, which effectively gives mechanical support to the DPE. © 1995 John Wiley & Sons, Inc.     

环氧树脂与氰酸酯共固化产物性能的研究

环氧树脂是一类综合性能优良并获广泛应用的热固性树脂基体 .但是通常的环氧树脂基体中含有大量反应生成的羟基等极性基团 ,吸湿率高 ,使其复合材料在湿热环境下力学性能和介电性能显著下降 .应用氰酸酯改性固化的环氧树脂等热固性树脂 ,将赋予以其为基体的复合材料以优异的耐热性能、力学性能和介电性能[1 ,2 ] .这类复合材料的研究开发对特种电子电气绝缘材料和先进复合材料的发展具有重要意义 .作者曾应用ＦＴ ＩＲ、ＤＳＣ等分析技术对氰酸酯与环氧树脂 (氰酸酯在欠量、适量和过量条件下 )的共固化反应机理和固化物结构特征等进行过深入…     

主链玻璃化转变区在室温附近的梳形聚合物电解质

主链玻璃化转变区在室温附近的梳形聚合物电解质＊齐力林云青夏永姚王佛松（中国科学院长春应用化学研究所长春１３００２２）关键词梳状高分子，固体电解质，离子导电性，玻璃化转变，分子运动＊１９９４－１０－３０收稿；１９９５－１２－１０修稿７３２高分子固体电解...     

Thermal,dielectric, and mechanical relaxation in poly(benzimidazole)/poly(etherimide) blends

Thermal, dielectric, and mechanical relaxation measurements on miscible blends of polybenzimidazole (PBI) and a polyetherimide (PEI, Ultem 1000) prepared by solution casting from dimethylacetamide (DMAc) reveal a number of structurally related features. Annealing below the glass transition temperature induces an enthalpy relaxation process typical of single-phase glasses of nonequilibrium structure. Dielectric relaxation experiments on samples annealed at ambient conditions reveal two relaxation processes below 400°C. At lower temperatures (50–200°C), the desorption of water is observed. Above 200°C in the first run, a composition-dependent relaxation is seen at the highest frequencies (100 kHz) while a relaxation approximately independent of composition appears in the second run. The latter corresponds to the glass transition of the PEI phase. The glass transition of PBI at this frequency is above the degradation temperature. At lower frequencies a strongly dispersive electrode polarization process masks the high-temperature relaxations. Dynamic mechanical results show similar features with respect to phase separation; the main difference is that the tan δ curves in the first run are complicated by the desorption of residual solvent.     

Dynamic mechanical analysis of ethylene tetrafluoroethylene (ETFE) foils in use for transparent membrane buildings

Glass transition temperature and tan delta (the ratio of loss modulus to storage modulus) are indispensable parameters for determining appropriate application range of ETFE foils. In this study, ETFE foils in terms of specimen number, material direction and thickness were investigated with dynamic mechanical analysis (DMA) over a temperature range of -70-100 °C at frequencies of 0.1, 1, and 10 Hz. Glass transition temperatures were obtained with storage modulus, loss modulus and tan delta curves. It is found that frequency effect on glass transition temperature was proportional and that frequency effect was more significant than material direction effect. Moreover, a comparison study showed that elastic modulus determined with quasi-static experiments was greater than storage modulus calculated with dynamic mechanical experiments. To propose suitable glass transition temperature ranges for engineering application, an approach to determine confidence interval based on statistical analysis was employed. The resulting intervals with confidence coefficient of 95% were 31.2–32.7 °C, 60.5–66.4 °C and 79.6–83.3 °C for storage modulus, loss modulus and tan delta, respectively. In general, this study could provide useful observations and values for evaluating dynamic mechanical properties of ETFE foils.     

Uniaxial tensile tests and dynamic mechanical analysis of satin weave reinforced epoxy shape memory polymer composite

The utilization of epoxy shape memory polymer composite (SMPCs) as engineering materials for deployable structures has attracted considerable attention in recent decades due to high strength and satisfactory stiffness in comparison with shape memory polymers (SMPs). Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery properties, especially for new epoxy SMPCs. In this paper, a new weave reinforced epoxy shape memory polymer composite was prepared with satin weave technique and resin transfer molding technique. Uniaxial tensile tests and dynamic mechanical analysis were carried out to obtain basic mechanical properties and glass transition temperatures, respectively.The tensile strength and breaking elongation of warp specimens were comparable with those of weft specimens. The increment of elastic modulus and hysteresis loop areas became smaller with loading cycles, meaning that cyclic tests could obtain approximate stable mechanical properties. For dynamic mechanical properties, glass transition temperature (T_g) obtained from storage modulus curves was lower than that determined from tan delta curves and T_gs in the warp and weft directions were similar (29.4 °C vs 29.7 °C). Moreover, the storage modulus in response to T_g was two orders of magnitude less than that with respect to low temperature, which demonstrated the easy processibility of epoxy SMPCs near glass transition temperature. In general, this study could provide useful observations and basic mechanical properties of new epoxy SMPCs.     

The proper glass transition temperature of amorphous polymers on dynamic mechanical spectra

Glass transition is crucial to the thermal and dynamical properties of polymers. Thus, it is important to detect glass transition temperature (T _g) with a sensitive and proper method. Dynamic mechanical analysis (DMA) is one of the most frequently used methods to determine T _g due to its advantage of high sensibility. However, there is controversy in the past literatures to determine the proper glass transition temperature among three transition temperatures, i.e., T _g1, T _g2 and T _g3 in the dynamic mechanical spectra, which correspond to the temperature abscissa of intersect value of two tangent lines on storage modulus (E′), the peak of the loss modulus (E″) and the peak of the loss tangent (tan δ). In this work, these three transition temperatures were compared with the glass transition temperature determined by DSC (T _gDSC). Based on the discussion of different modes of molecular motion around the glass transition region, it is demonstrated that T _g1 and T _g2 have the same molecular mechanism as T _gDSC, i.e., local segmental motion which is enthalpic in nature and determines the proper glass transition temperature, while T _g3 is assigned to the transition temperature of entropic Rouse modes, thus cannot be used as the proper glass transition temperature.     

Molecular Structures and Mechanical Properties of Microbe Rapid Coagulation Natural Rubber

In this work,molecular structures,dynamic mechanical properties and glass transition temperatures of microbe coagulated natural rubber(NR) samples were analyzed by using pyrolysis gas chromatography-mass spectrometry(py-GC/MS),rubber process analyzer(RPA) and dynamic mechanical thermal analysis(DMA).And the cross-linked network structures and mechanical properties of the corresponding NR vulcanizates were further determined by using nuclear magnetic resonance(NMR) crosslink density spectrometer(XLDS-15) and universal testing machines.The results show that NR raw rubber produced by rapidly coagulated with microorganism exhibits a simple molecular structure composition and good dynamic mechanical properties,and the corresponding NR vulcanizates possess the aggregation structure of high cross-linked density,a high glass transition temperature of-61.5 ℃ and high mechanical properties(tensile strength reaches 25.2 MPa),as compared with that coagulated with acetic acid.     

Dynamic mechanical studies of endgroup-modified polystyrene

Polystyrenes having both modified and unmodified endgroup structures were synthesized. These polystyrenes were then subjected to dynamic mechanical testing below their glass transition temperature. The modified structures were shown to influence the β transition of polystyrene. While the mechanism of this secondary transition has been speculated but never unequivocally substantiated in the past, the evidence presented here strongly support the idea that the β transition of polystyrene arises from chain-end motions.     

Broadened glass transition in a liquid-crystalline polymer studied by thermally stimulated currents,AC dielectric,dynamic mechanical,and DSC methods

Thermally stimulated currents (TSC), a. c. dielectric, dynamic mechanical (DMTA), and differential scanning calorimetry (DSC) methods were used to study the glass transition in a thermotropic liquid-crystalline copolyester. All the techniques were consistent in the determination of the main glass transition temperature. Using the high sensitivity of the TSC thermal sampling method, it was shown that cooperative glass transition-like relax-ations occur down to 100°C below the main glass transition. DSC was sensitive only to a broadening of the glass transition to about ca. 30°C, so it was concluded that the thermal sampling method is sensing a very small fraction of cooperatively relaxing species which cannot be detected by DSC. Ac dielectric measurements and DMTA also indicated that the glass transition was broad, but difficulties with overlapping transitions prevented quantitative determination of the breadth of the glass transition. The results suggest that the broad glass transition, in this mostly amorphous LCP, is due to chemical heterogeneity of the copolyester chain. Other evidence indicates that the broadening is not due to the oriented nature of the glassy state. Some discussion is presented concerning how the heterogeneous nature of the LCP glass leads to compensation of the Arrhenius curves obtained by the thermal sampling method. © 1993 John Wiley & Sons, Inc.     

DYNAMIC MECHANICAL RESPONSE OF CRAZES IN POLYSTYRENE

Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which is assigned to glass transition peak of craze fibrils. The decreaseof glass transition temperature of polymer in craze fibrils is due to the high values of surface tovolume ratio. The glass transition temperature ratio of craze fibrils to bulk material (T_g~l /Tg) hasbeen expressed as a function of the fibrils diameter (d). From T_g~l of craze fibrils,the value of fibrildiameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrilsplastically deform and cause the fibrils to thin slightly,whereas annealing the crazed specimen atthe temperature near T_g of the craze fibrils makes the fibrils bundle together.     

聚氨酯制备的多尺度模拟方案

针对聚氨酯材料特性设计了多尺度计算机模拟方案, 并研究了不同原料及相同原料但不同官能度对所制备的聚氨酯材料力学性能和玻璃化转变温度的影响. 基于原子级别的结构, 建立了耦合聚合反应的粗粒化耗散粒子动力学模型来描述组分扩散及交联网络结构的形成过程. 并反映射这个粗粒化结构到全原子级别来分析材料的力学性能和热力学性能. 这个多尺度研究方案也可推广到研究多个竞争性因素同时主导的复杂体系中.     

聚氨酯制备的多尺度模拟方案

针对聚氨酯材料特性设计了多尺度计算机模拟方案,并研究了不同原料及相同原料但不同官能度对所制备的聚氨酯材料力学性能和玻璃化转变温度的影响.基于原子级别的结构,建立了耦合聚合反应的粗粒化耗散粒子动力学模型来描述组分扩散及交联网络结构的形成过程.并反映射这个粗粒化结构到全原子级别来分析材料的力学性能和热力学性能.这个多尺度研究方案也可推广到研究多个竞争性因素同时主导的复杂体系中.