环氧化三元乙丙橡胶增韧聚对苯二甲酸丁二酯的脆韧转变

环氧化的三元乙丙橡胶(eEPDM)与聚对苯二甲酸丁二酯(PBT)共混可以使PBT共混体的缺口冲击强度获得很大的提高.当eEPDM橡胶浓度为24wt%时,PBTeEPDM共混体的缺口冲击强度是纯PBT的12倍.随着eEPDM含量的增加,在室温下PBTeEPDM共混体出现了明显的脆韧转变,其脆韧转变的临界粒子间距为0.49μm.橡胶的加入及含量的增加使PBT体系的脆韧转变温度(TBD)向低温移动,且PBTuEPDM与PBTeEPDM共混体脆韧转变温度的差随橡胶含量的增加而逐渐增大.扫描电镜照片表明,在橡胶组成相同的情况下,PBT基体中分散的eEPDM粒子明显小于未环氧化的EPDM粒子.且eEPDM橡胶的粒子间距(ID)也明显地低于uEPDM橡胶粒子的ID,这导致PBTeEPDM共混体系在室温下出现脆韧转变.     

Enhanced mechanical and shape memory properties of polyurethane block copolymers chain-extended by ethylene diamine

Effect on shape memory and mechanical properties of polyurethane (PU) copolymers by changing the chain extender from 1,4-butanediol (BD) to ethylenediamine (ED) was investigated. PU copolymers composed of the different ratio of hard and soft segment were prepared and characterized by IR, DSC, XRD, and UTM. Glass transition temperature of PU increased to room temperature range by adopting ED as a chain extender. The XRD peak pattern changed with hard segment content. ED type PU achieved the high mechanical properties at lower hard segment content than BD type PU. Especially, strain at break of ED type significantly improved compared to BD type. Shape recovery rates were similar for both types of PU, but ED type showed better shape retention rate than BD type. The reason for the differences between two types of PU is discussed in this paper.     

固态高聚物状态方程的研究

本文从理论上导出了一个新的三参数固态高聚物的状态方程:P=(B_0/4.98)[((V_0/V))~(7.14)-((V_0/V))~(2.16)+(T/T_0)]在不发生转变的情况下,它适用于描述固态高聚物的压强—体积—温度关系,方程形式简单,参数物理意义明确.     

Adiabaticity Conditions for the Process of Stretching of Uniformely Deforming Polymers

Plastic deformation of polymers is accompanied by increasing temperature owing to the transformation of mechanical work for the deformation into heat. The effect of the strain rate on the heating of uniformly deforming polymer films is analyzed theoretically. A formula describing the heating value is derived. As in the case of a frontal spreading of the neck, an increase in the strain rate upon a uniform deformation results in the transition from an isothermal process to an adiabatic one. The rate of the transition to adiabatic strain conditions increases with a growth of deformation. As compared to the neck spreading process, the transition is shifted toward higher strain rates. At low elastic deformations and usual rate values, the strain proceeds in an adiabatic regime.     

可生物降解多嵌段聚(酯-氨酯)的合成及其热致形状记忆性质

以端羟基L-丙交酯/乙交酯共聚物(PLLG-diol)和端羟基ε-己内酯/乙交酯共聚物(PCG-diol)为硬段和软段,通过与二异氰酸酯反应制得了软、硬分子量和组成均可调的多嵌段聚(酯-氨酯),表征了它们的形状记忆行为.多嵌段聚(酯-氨酯)具有良好的形状记忆性质,应变固定率达98%~99.5%,应变恢复率达93%~98.5%;通过转变温度的调节,可使多嵌段聚(酯-氨酯)在37℃体温下不发生形状变化,而在稍高于体温的温度(40~50℃)下恢复原始形状,其形状恢复速率可通过温度和升温速率来调节.     

The brittle-ductile transition in rubber-filled polymers

Composites based on various polymers and rubber particles as a filler were studied. As the filler concentration was increased, the transition from necking to brittle fracture and then to uniform ductile yielding was observed. The criterion for the brittle-ductile transition, which is accompanied by an increase in the elongation at break, is equality between the tensile strength and the upper yield stress of the filled composite. Upon the brittle-ductile transition, the critical concentration of rubber particles is determined by two parameters: the height of the yield drop (difference between the upper and lower yield stresses of matrix polymer) and adhesive strength at the interface between the matrix polymer and filler particles (in the case of good adhesion, tensile strength of rubber particles). The larger the yield drop, the broader the concentration range corresponding to the polymer brittle fracture. The enhancement of adhesion between the matrix and the particles makes it possible to displace the brittle-ductile transition to lower filler contents and, hence, to narrow the region of brittle fracture of the composite.     

相容剂对PP/POE共混体系脆韧转变行为的影响

采用熔融挤出法制备了不同相容剂含量的PP/POE共混体系,测试了不同体系的脆韧转变温度、热性能和力学性能.结果表明,乙烯-丙烯多嵌段共聚物相容剂的加入降低了PP/POE共混物的脆韧转变温度,提高了共混物的韧性.AFM和STEM照片显示相容剂的加入减小了橡胶分散相的临界粒子间距,PP和POE在两相界面结合处相互扩散或渗透,实现了POE弹性体在PP树脂中合适的尺度分布以及良好的形态分散.当相容剂含量达到10％时,POE分散相尺寸细小均匀,分散相粒子粒径为0.54μm,粒子间距为0.1 μm,PP结晶链段更多地插入到弹性体内部,弹性体POE分散相形成明显的“硬核-软壳”结构.DSC曲线中结晶峰和熔融峰的变化说明适量的相容剂对于材料结晶度的提高具有一定的促进作用.力学性能测试结果可以看出相容剂的加入在提高材料韧性,降低其脆韧转变温度的同时也保持了材料的刚性性能.     

Comparison of the transient stress–strain response of rubber to its linear dynamic behavior

Master curves of the small strain and dynamic shear modulus are compared with the transient mechanical response of rubbers stretched at ambient temperature over a seven‐decade range of strain rates (10^?4 to 10³ s^?1). The experiments were carried out on 1,4‐ and 1,2‐polybutadienes and a styrene–butadiene copolymer. These rubbers have respective glass transition temperatures, T_g, equal to ?93.0, 0.5, and 4.1 °C, so that the room temperature measurements probed the rubbery plateau, the glass transition zone, and the onset of the glassy state. For the 1,4‐polybutadiene, in accord with previous results, strain and strain rate effects were decoupled (additive). For the other two materials, encroachment of the segmental dynamics precluded separation of the effects of strain and rate. These results show that for rubbery polymers near T_g the use of linear dynamic data to predict stresses, strain energies, and other mechanical properties at higher strain rates entails large error. For example, the strain rate associated with an upturn in the modulus due to onset of the glass transition was three orders of magnitude higher for large tensile strains than for linear oscillatory shear strains. © 2011 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys, 2011     

Heating of polymers during neck propagation

The heating of polyethylene terephthalate, polyamide-66, and polyamide-6 during tensile drawing at room temperature was studied theoretically and experimentally. At a low draw rate, the necking temperature was close to the temperature of the surrounding air. An increase in the rate results in the transition to the adiabatic conditions of drawing. A necking temperature of 140°C was experimentally recorded in polyethylene terephthalate at a draw rate of 1000 mm/min and during the approach to the adiabatic conditions of drawing. A formula describing the dependence of the necking temperature on the draw rate was derived. The resulting value agreed fairly well with the theoretical estimation of the temperature. The drawing (strain) ratio in the neck and the draw stress are the crucial parameters determining the temperature. The rate of the transition to the adiabatic conditions of drawing was determined. The temperatures of adiabatic heating for various polymers were calculated. The increases in the temperatures of polycarbonate and low- and high-density polyethylene are relatively low. The increases in temperature can be regarded as moderate for polypropylene and polyvinyl chloride, while they attain the highest values in polyamide-6 and polyethylene terephthalate owing to the high draw ratios in the neck and the high draw-stress values.     

On the scaling law of the evolution of lap-shear strength with healing temperature at amorphous polymer−polymer interfaces and surface glass transition

The evolution of lap-shear strength (σ) with healing temperature T _h at symmetric and asymmetric amorphous polymer−polymer interfaces formed of the samples with vitrified bulk has been investigated. It has been found that the square root of the lap-shear strength behaves with respect to healing temperature as σ ^1/2 ~ T _h both at symmetric and asymmetric interfaces. Basing on this scaling law between σ and T _h, the values of the surface glass transition temperature ( T_g^surface ) \left( {T_{\rm{g}}^{\rm{surface}}} \right) have been estimated for a number of amorphous polymers by the extrapolation of the experimental curves σ ^1/2 ~ T _h for symmetric polymer−polymer interfaces and, in some cases, for asymmetric, both compatible and incompatible, polymer−polymer interfaces, to zero strength. A significant reduction in surface glass transition temperature T_g^surface T_{\rm{g}}^{\rm{surface}} with respect to the glass transition temperature of the polymer bulk ( T_g^bulk ) \left( {T_{\rm{g}}^{\rm{bulk}}} \right) , reported earlier, has been confirmed by the use of the new proposed approach. The quasi-equilibrium surface glass transition temperature T_g^surface T_{\rm{g}}^{\rm{surface}} of amorphous polystyrene (PS) has been predicted in the framework of an Arrhenius approach using the plot “logarithm of healing time − reciprocal surface glass transition temperature T_g^surface￠￠ T_{\rm{g}}^{\rm{surface}}\prime \prime and the activation energy of the surface alpha-relaxation of PS has been calculated.     

异氰酸光解的动态学研究

在异氰酸光解势能面研究的基础上,计算了不同电子态热能面交叉点S_1/T_1 处S_1 → T _1的态-态积累跃迁速率k_(S_1→T_1),S_1/S_0处S_1 → S_0的跃迁 速度k_(S_1→S_0),结果表明,在交叉点处态-态跃迁速度非常大,可以认为高能 态在交叉点可以直接跃迁到低能态。据此我们又根据单分子微正则过渡态理论计算 了不同光解波长下S_1态和T_1态的光解反应速度k_反~(S_1)（E）和k~(T_1)（E） 和S_1态反-顺异构化的反应速率。在光解波长为230 nm时,k_(T_1)/k_(S_1) = 9. 48,与实验值为5相接近;在低能时k~(T_1) > k_反~(S_1),获得了和实验相一致 的结果。     

不同初始结构间规聚丙烯纤维熔融过程中的结晶转变行为

通过熔融纺丝及随后的热处理制备了具有不同初始结构的间规聚丙烯纤维(sPP).采用差示扫描量热仪(DSC)和变温广角X-射线衍射仪详细研究了sPP纤维在升温过程中的结构转变和熔融行为.结果表明,不同初始结构sPP纤维的晶型不同,卷绕纤维和退火处理纤维以Ⅰ型和Ⅱ型晶型为主,牵伸纤维介晶相占优;升高温度导致Ⅰ型和Ⅱ型两种晶型直接熔融,没有出现Ⅱ型向Ⅰ型的晶型转变;初始结构为介晶相的纤维在升温过程中部分介晶相直接转变为Ⅱ型晶型,还有一部分介晶相直接熔融,并在随后的升温过程中,形成Ⅰ型晶型.sPP纤维的多重熔融行为与其初始结构和纤维制备条件密切相关.     

On the formation of topological entanglements during the contact of glassy polymers

Fracture energy (G) of the symmetric amorphous polystyrene (PS)–PS interfaces that were partially healed at temperatures (T) below the glass transition temperature of the bulk ( $ T_{\text{g}}^{\text{bulk}} $ ) has been measured at ambient temperature and compared with those reported in the literature (G ₀) for the symmetric PS–PS interfaces that were fully healed at T?>? $ T_{\text{g}}^{\text{bulk}} $ . It has been shown that G developed at T?<? $ T_{\text{g}}^{\text{bulk}} $ corresponds to G ₀ for the polymers having the molecular weight larger than the entanglement molecular weight. This behaviour indicates that topological entanglements can be formed across the contact zone of the polymers with glassy bulk via the interdiffusion of the chain segments located in the viscoelastic contact layer.     

Micro-Raman study of the transition front in uniaxially stretched semicrystalline polymers

The transition front of the neck between the isotropic and oriented region in uniaxially stretched polyvinylidene fluoride (PVDF) and polypropylene (PP) is analyzed with a high spatial resolution by micro-Raman spectroscopy. The variation of the microstructure, i.e. change in the degree of crystalline modification in the case of PVDF and in the orientation of the PP chains in function of the strain rate, is correlated with other parameters associated with the drawing response of these polymers and the temperature rise during deformation. The results here described can be understood through the clear increase of temperature that was detected in the neck due to the heat generated by the deformation work of the drawing process.     

Tensile mechanical properties of basalt fiber reinforced polymer composite under varying strain rates and temperatures

High-strength woven fabrics and polymers are ideal materials for use in structural and aerospace systems. It is very important to characterize their mechanical properties under extreme conditions such as varying temperatures, impact and ballistic loadings. In this present work, the effects of strain rate and temperature on the tensile properties of basalt fiber reinforced polymer (BFRP) were investigated. These composites were fabricated using vacuum assisted resin infusion (VARI). Dynamic tensile tests of BFRP coupons were conducted at strain rates ranging from 19 to 133 s⁻¹ using a servo-hydraulic high-rate testing system. Additionally, effect of temperature ranging from −25 to 100 °C was studied at the strain rate of 19 s⁻¹. The failure behaviors of BFRP were recorded by a Phantom v7.3 high speed camera and analyzed using digital image correlation (DIC). The results showed that tensile strength, toughness and maximum strain increased 45.5%, 17.3% and 12.9%, respectively, as strain rate increased from 19 to 133 s⁻¹. Moreover, tensile strength was independent of varying temperature up to 50 °C but decreased at 100 °C, which may be caused by the softening of epoxy matrix and weakening of interfaces between fibers and matrix when the glass transition temperature was exceeded.     

An investigation of the yield and postyield behavior and corresponding structure of poly(methyl methacrylate)

The mechanical behavior of glassy polymers is time and temperature dependent as evidenced by their viscoelastic and viscoplastic response to loading. The behavior is also known to depend strongly on the prior history of the material, changing with time and temperature without chemical intervention. In this investigation, we examine the effects of this process of physical aging on the yield and postyield behavior and corresponding evolution in the structural state of glassy polymers. This has been achieved through a systematic program of uniaxial, isothermal, constant strain–rate tests on poly(methyl methacrylate) (PMMA) specimens of different thermal histories and by performing positron annihilation lifetime spectroscopy (PALS) measurements prior to and after mechanical deformation. PALS is an indicator of the free volume content, probing size and density of free volume sites and can be considered to be a measurement of structural state. The results of the mechanical tests show that aging acts to increase both the initial yield stress and the amount of strain softening which occurs subsequent to yield. Moreover, the amount of strain softening was found to be independent of strain rate indicating that softening is related to an evolution in structure as opposed to deformation kinetics. Furthermore, after sufficient inelastic straining, the initial thermal history is completely erased as evidenced by identical values of flow stress following strain softening, for both annealed and quenched polymer. Strong confirmation of the structural state or free volume related nature of the strain softening process is obtained by our companion PALS measurements. PALS detects an increase in the size of free volume sites following inelastic deformation and finds the initially annealed and quenched specimens to posses the same post-deformation distribution. The size of sites is found to evolve steadily with inelastic strain until it attains a steady-state value. This evolution of free volume with strain follows the observed softening of the flow stress to a steady-state value. These results provide experimental evidence that an increase in free volume with inelastic straining accompanies the strain softening phenomenon in glassy polymers and that strain softening is indeed a de-aging process. Based on our experimental results a mechanistically based constitutive model has been formulated to describe the effects of thermal history on the yield and postyield deformation behavior of glassy polymers up to moderate strains. The model is found to successfully capture the effects of physical aging, strain softening, strain rate, and temperature on the inelastic behavior of glassy polymers when compared with experimental results. © 1993 John Wiley & Sons, Inc.     

Thermal conductivity behaviour of polymers around glass transition and crystalline melting temperatures

The thermal conductivity of five semi-crystalline and four amorphous polymers was determined within a wide range of temperature, starting at room temperature and going up to temperatures above the polymer melting point (Tm) for semi-crystalline polymers or above the glass transition temperature (Tg) for amorphous polymers. Two transient techniques were employed in the experimental investigation: the hot wire technique for the group of amorphous polymers, and the laser flash technique for the semicrystalline polymers. As expected, the experimental results show that Tg exerts a measureable influence on the thermal conductivity of amorphous polymers. In the case of semi-crystalline polymers, a singular behaviour of the thermal conductivity is observed within the Tm range. In order to explain the anomalous behaviour, the influence of these transition temperatures on the thermal conductivity behaviour with temperature has been analysed in terms of a phonon conduction process and temperature variations of specific heat and modulus of elasticity of the analyzed polymers.     

DTA中升温速率及样品热导率对T_g测量值影响的模拟研究

就不同升温速率和实际样品的不同热导率对差热分析 (DTA)中高分子材料的玻璃化转变曲线的影响进行了MonteCarlo模拟研究 ,发现当所有样品刚完成玻璃化转变时 ,在Tg 曲线中该特征点要低于Tg 的转变中点。转变中点所对应的样品温度肯定要高于实际的玻璃化转变温度。如果以玻璃化转变曲线的转变中点所对应的样品温度作为该材料的玻璃化转变温度 ,那么 ,升温速率越快、样品的热导率越小 ,所测得的玻璃化转变温度就越大 ,反之亦然。DTA测得的玻璃化转变温度与升温速率间有很好的线性依赖关系 ,但与样品热导率间的关系是非线性的     

氰酸酯树脂改性热固性丁苯树脂的固化及其动力学

利用傅里叶变换红外光谱法(FT-IR)和差示扫描量热法(DSC)研究了氰酸酯树脂改性热固性丁苯树脂的固化反应特性及其动力学.以温度-升温速率外推法计算得到固化反应起始温度(Ti0)、峰顶温度(Tp0)和终止温度(Tf0)分别为414.2、444.5、460.6 K,对改性树脂的固化过程进行优化.采用Freeman-Ca...