Morphology development in PS/LLDPE blend during and after elongational deformation

The morphology development within a PS/LLDPE blend with 5 wt % of LLDPE at various stages of uniaxial deformation and after cessation of the flow was studied. Under given deformation conditions the dispersed LLDPE particles stretch and form highly elongated fibrils in agreement with a modified capillary number model. The morphology development after deformation was investigated for two different modes—relaxation and recovery. It was found that the stress in the sample is the crucial parameter determining the morphology development. During the first part of relaxation the stress in the sample is sufficient to hold the particles in the highly elongated state and, therefore, Rayleigh breakup takes place according to the Tomotika theory. It results in considerably finer phase structure. Contrary to this, in the absence of the stress in the sample, that is, in the recovery mode, the fibrils start to shrink immediately after the deformation and after a certain time the spherical morphology is restored. During elongation and recovery no evidence of coalescence was observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 16–27, 2008     

Chain elongation of monosaccharides by sequential cross metathesis and asymmetric dihydroxylation: expeditious approach to higher sugars

Glucose-derived alkenes were homologated via chain elongation to afford higher sugars by the application of cross metathesis with an alkene followed by Sharpless asymmetric dihydroxylation. Heptose, octose, nonose, and decose derivatives were expeditiously prepared by this method.     

Mechanical,thermal and rheological properties and morphology of poly (lactic acid)/poly (propylene carbonate) blends prepared by vane extruder

In this study, the poly (lactic acid) (PLA) and poly (propylene carbonate) (PPC) blends with different compositions were prepared by a novel vane extruder based on elongation rheology. The mechanical properties, morphologies, crystallization behavior, thermal stability, and rheological properties of the blends were investigated. Mechanical test showed that PLA could be toughened by PPC to some extent, and the impact strength of the PLA was maximized when PPC content was about 30%. Differential scanning calorimetry analysis revealed that PPC had little effect on the melting process, the crystallization behavior of PLA component in the blend was improved, and the cold crystallizability of PLA decreased with the increase of PPC content when the PPC content was less than 50%. Thermogravimetry analysis showed that the thermal stability of the blends was improved by compounding with PLA. Scanning electron microscope showed that the dispersion of PLA droplets in PPC matrix was better than that of PPC droplets in PLA matrix. Rheological test showed that the melt viscosity of the pure PLA and the blend with 10% PPC was insensitive to shear rate, and the blends melt appeared shear thinning phenomenon with the increase of PPC content. It also showed that the blends microstructure changed with the addition of PPC and the blends with PPC content in a certain range had similar stress relaxation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.     

Electron microscopic investigations of the structure of crazes in polystyrene

The structures of the deformation zones in polystyrene (PS), the so-called crazes, were investigated in detail by electron microscopy. Compared with the conventional transmission electron microscope (TEM) the usage of a high voltage electron microscope (HVEM) with an accelerating voltage of 1000 kV has several advantages: it renders possible the investigation of relatively thick specimens (thicknesses up to and exceeding 5 m), the performance ofin situ deformation tests, and the application of a special tensile device, producing a defined uniaxial straining state.First, general features of the crazes in PS (pressure-molded samples, solution-cast films) are described, and second, the crazes are precisely characterized by quantitatively measuring the electron micrographs of the crazes. Shape, thickness profile, minimum size, interior structure, and elongation of the crazes are discussed in detail.     

无活化剂存在时己内酰胺碱催化聚合及高延伸铸型尼龙的制备

研究了在无活化剂存在时己内酰胺的碱性催化聚合反应。实验结果表明当聚合温度在190—220℃范围时制备的铸型尼龙其断裂伸长率在200％以上,最高达363％。并具有高耐冲击性能。与一般铸型尼龙相比较,该高延伸铸型尼龙具有较低的抗张强度、弹性模量、熔点、玻璃化转变温度、密度和结晶度。     

Energy balance in networks simply elongated at constant temperature

Summary Mechanical and thermal energy exchange in isothermal simple elongation experiments on various rubbers observed by Godovsky can fully be described by means of implicit relations which are defining the thermo-elastic properties of van der Waals networks up to highest elongations. Global and local properties in the molecular networks are shown to be uniquely related thus manifesting indirectly the existence of a Gibbs-function.Symbols f force per unit unstrained area - f _s,f _e entropy- or enthalpy component of the deformational stress - N density of crosslinks - k Boltzmann's constant - T absolute temperature - L ₀ fiducial length - < ²> actual mean-square end-to-end distance - < ₀> mean-square end-to-end distance of the equivalent free chains - () deformation function - D=/ derivative of() - strain parameter - _m maximum strain - a ₁,a ₂ interaction — van der Waals parameters - linear coefficient of thermal expansion - linear coefficient of compressibility - V ₀ volume in the unstrained state of the rubber - h _K ⁽ⁱ⁾ ,s _K ⁽ⁱ⁾ specific enthalpy and entropy of the internal freedom (K)     

A fracture criterion of rubber-like materials under plane stress conditions

In this work, we attempt to derive a fracture criterion for filled and unfilled elastomer vulcanizates and thermoplastics from a set of experimental data. Firstly, fracture criteria reported in the literature have been applied to experimental data obtained from tests including various loading modes (simple tension, equal biaxial tension and biaxial tension) and performed on four materials: a natural rubber (NR), a styrene butadiene rubber (SBR), a polyurethane (PU) and a thermoplastic elastomer (TPE).

Then, a new failure criterion based on an equivalent elongation concept is proposed. This equivalent elongation seems to be linearly dependent on a given biaxiality ratio n=(ln(λ_2b)/ln(λ_1b)), which leads to expressing the principal elongations at break as functions of both the biaxiality n and two experimental parameters. Quite good agreement is highlighted when comparing the failure experimental data with the proposed criterion for the tested elastomers.     

Biodegradable network elastomeric polyesters from multifunctional aromatic carboxylic acids and poly(ϵ‐caprolactone) diols

Novel biodegradable network polyesters were prepared from multifunctional aromatic carboxylic acids [trimesic acid (Y), pyromellic acid (X), and mellic acid (Y_M)] and poly(?‐caprolactone) (PCL) diols with molecular weights of 530, 1250, and 2000. Prepolymers prepared by a melt polycondensation method were cast from dimethylformamide solutions and postpolymerized at 220 °C for various times to form a network. The resultant films were transparent, flexible, and insoluble in organic solvents. The network polyesters obtained were characterized by infrared absorption spectra, wide‐angle X‐ray diffraction analysis, density measurements, differential scanning calorimetry, thermomechanical analysis, and tensile testing. Some network polyester films, including YPCL_1250, XPCL₁₂₅₀, and Y_MPCL₂₀₀₀, showed elastomeric properties with high ultimate elongation and low tensile modulus. The enzymatic degradation was measured by the weight loss of the network polyester films in a buffer solution with Rhizopus delemar lipase at 37 °C. The degree and rate of degradation increased with the increasing molecular weight of the PCL diols, but they decreased in the order of YPCL > XPCL > Y_MPCL because of the increase in the crosslinking densities of the network films. The degraded products after enzymatic degradation showed that the ester linkage of the PCL component and the aromatic ester linkage between Y and PCL diols were hydrolyzed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4523–4529, 2002     

单宁作为共引发剂和交联剂制备高伸长率水凝胶

以过硫酸铵为引发剂(APS)、杨梅综合单宁(TA)作为共引发剂和交联剂,通过自由基聚合制备了高伸长率水凝胶(TIC-gel)。通过红外光谱(FT-IR)、核磁共振(~1 H-NMR)和浸泡尿素的方法研究了TA在TIC-gel中形成化学交联的机理。通过拉伸、压缩测试和流变学测试系统地分析了TIC-gel的力学性能和影响因素。结果表明:相比于传统化学交联水凝胶(PAM-MBA-gel),利用TA制备的凝胶具有高伸长率(2 250%)和高韧性(3.51 MJ/m3)。利用这一新的形成交联的方法所得的凝胶即使在高浓度时也能形成均匀的结构,可以很好地分散应力,为TIC-gel的高伸长率作出贡献。