Controlling Necking in Extrusion Film Casting Using Polymer Nanocomposites

The research described was concerned with the effect of layered-silicate-based organically modified nanoclay fillers on controlling the extent of necking in a polymer melt extrusion film casting (EFC) process. We show that a linear polythylene resin (such as a linear low-density polyethylene—LLDPE) filled with a very low percentage of well-dispersed (or intercalated) nanoclay displays an enhanced resistance to the necking phenomenon. In general, melt-compounded nanoclay-filled LLDPE resin formulations displayed a higher final film width (less necking), thus a lower final film thickness (greater draw down for the same draw ratio), and cooled down faster when compared to the base LLDPE resin. Incorporation of nanoclay filler in the mainly linear chain LLDPE resin led to significant modification of the melt rheological properties that, in turn, affected the melt processability of these formulations. Primarily, the intercalated nanoclay-filled LLDPE formulations displayed the presence of strain-hardening in unaxial extensional rheology. Additionally, the presence of well-dispersed nanoclay in the LLDPE resin led to a display of prominent extrudate swell indicating the presence of melt elasticity in such formulations. The presence of melt elasticity, as shown by shear rheology and strain-hardening, observed by uniaxial extensional rheology, contributed to the LLDPE nanoclay formulations displaying an enhanced resistance to necking for these films. It can be concluded that linear chain polymers susceptible to necking in an EFC process can be made more resistant to such necking by using nanoclay fillers at very low levels of loading.     

Sasobit对SBS改性沥青性能的影响研究

为揭示温拌剂Sasobit对SBS改性沥青性能的影响,本文分别进行了不同温拌剂含量沥青的三大指标、布氏粘度、粘温扫描、动态剪切流变和低温弯曲流变等试验。结果表明:Sasobit使SBS沥青软化点降低,虽然其温度敏感性增大,但对针入度和延度影响不大。温拌沥青在105℃以上高温区粘度明显下降,这对施工有利;但随温度的降低,粘度却比原样提高,这对实际使用有利。依据三大指标和粘度试验结果,本文提出SBS沥青的Sasobit最佳掺量为3%。粘温扫描曲线显示,含Sasobit沥青粘度增大,特别是在75℃以下的温度区域,这对夏季抗车辙有利。此外,温拌剂Sasobit使SBS沥青的PG分级的高温等级提高,而对低温等级影响不大。     

Functional Features of Alginates Recovered from Himanthalia elongata Using Subcritical Water Extraction

Subcritical water extraction of Himanthalia elongata and the subsequent acetone fractionation to precipitate crude fucoidans generated a liquid phase which was used to recover alginates with a wide range of viscoelastic features and other soluble extracts with potential biological activities. The precipitated alginate was converted to sodium alginate using an environmentally friendly treatment before being characterized by Fourier transform infrared attenuated total reflectance, nuclear magnetic resonance, high performance size exclusion chromatography and rheological measurements. The cell viability of three human cell lines (A549, HCT-116, T98G) in the presence of the extracts obtained before and after acetone fractionation was assessed. Fractionation with different acetone volumes showed a slight effect in the behavior of the different tested cell lines. Results also indicated a notable effect of the processing conditions on the block structure and molar mass of the extracted biopolymer, with the subsequent impact on the rheological properties of the corresponding gelled matrices.     

Review of nonlinear oscillatory shear flow notations and presentations: polymeric liquids

We review notations for, along with ways of presenting, the shear stress responses to large-amplitude oscillatory shear flow (LAOS). We find that the Fourier loss and storage viscosities to be the simplest primal notations for interpreting LAOS. The relative intensities provide the best evidence for oscillatory shear entering the large-amplitude regime. Deviation from linear viscoelastic behaviors can be observed through the distortions of Lissajous loops. We explore these loops in their elastic and viscous projections. The centerpiece of this work is our review table, which summarizes experimental measurements for polymer melts and solutions, targeting 21st century publications. Our review also provides conversion formulae to go from any of many notations to the Fourier loss and storage viscosities. The review table also defines which part of the LAOS measurement field has yet to be ploughed and shines light on which notations have been used, and for which purposes, to interpret nonlinearities.     

Collapse mechanisms and extreme deformation of particle-laden interfaces

Particle-laden interfaces are at the basis of many advanced materials, such as bijels and dry water. While the final properties of these materials can generally be controlled, their response to deformation during processing and use is still poorly understood. In particular, the dynamics of particle-laden interfaces in relevant flow conditions is receiving increasing attention. These conditions are typically highly dynamic and can involve unsteady flow or large deformations. This article gives an overview of the remarkable phenomena of particle-laden interfaces undergoing deformations of large amplitude and at high strain rate, in other words extreme deformation. Upon large-amplitude compression, a monolayer of particles can collapse by buckling or by expelling particles in the liquid. The criteria for buckling or expulsions, as well as recent experiments in highly dynamic conditions, are discussed, showing that these criteria can depend also on the rate of deformation. The emerging use of ultrasound-driven bubbles as an experimental platform for controlled deformation of particle-laden interfaces at high strain rate is also discussed. The ability to control the fate of particles at interfaces during dynamic deformation of droplets or bubbles ultimately underpins a variety of applications from controlled release to catalysis.     

Controlled Synthesis,Characterization, and Flow Properties of Ethylene–Diene Copolymers

The flow response of branched entangled resins is dominated by the branching topology of the constituent molecules, a property that is not directly accessible using experimental analytical tools for industrially relevant complex resins. In this paper, the controlled terpolymerization of ethylene, 1,9‐decadiene, and either hexene or octene in a continuous stirred tank reactor with a metallocene catalyst, is reported. The synthesized samples are characterized extensively with various analytical tools and their rheological properties are measured with small amplitude oscillatory shear and start‐up uniaxial extension experiments. A model is developed for the polymerization process with the mass balance during synthesis providing strong constraints on the rate constants. In silico ensembles of molecules, generated via Monte Carlo sampling, are used to reproduce the experimental results. The computer model allows us to infer the detailed branching structure of the molecules and to predict the optimum range of reactor conditions for this synthesis.     

冰水浴和自然冷却条件下锂基润滑脂的流变学性能

通过两种不同冷却方式制得锂基润滑脂,采用HAAKE流变仪考察了锂基润滑脂的流变特性,从流变学的角度分析了润滑脂在动态条件下的实时变化,并与其胶体安定性和机械安定性等性能进行了比较.结果表明:锂基润滑脂的流变性能可以很好地反映出润滑脂的胶体安定性和机械安定性;在测试应力范围内,于自然冷却条件下制备的润滑脂结构变化为可逆变化,而冰水浴制备的润滑脂结构容易遭到不可逆的破坏.     

弛豫法研究预交联颗粒凝胶的界面扩张流变性质

采用界面张力弛豫方法研究了一种新型聚合物--预交联颗粒凝胶(PPG)的界面流变性质, 考察了电解质及传统直链聚丙烯酰胺与PPG的相互作用对体系界面性质的影响, 计算得到了各体系界面扩张弹性和黏性的全频谱, 并通过归一法计算得到了相应的Cole-Cole图. 结果表明, 随着体相浓度的增加, PPG在界面层中形成网络结构, 界面扩张弹性和黏性大幅增强. 电解质能够中和PPG结构中的电荷, 明显降低扩张弹性和黏性. 直链聚丙烯酰胺与PPG在界面上可能形成更为复杂的结构, 膜的黏弹性由PPG决定.     

壬基酚聚氧乙烯醚(10)/水体系层状液晶的流变性

采用应力控制流变仪,研究了非离子表面活性剂壬基酚聚氧乙烯醚(10)(NP-10)/水体系层状液晶在不同温度和表面活性剂质量分数的流变性。 在线性黏弹区内,其储能模量和损耗模量与频率的关系不符合Maxwell模型,并用滑移模型、范德华力、水化作用解释了非离子表面活性剂层状液晶表现此类流变性的原因;用Burgers模型解释了蠕变-回复实验的结论,其结果与线性的振荡实验一致。     

A Novel Liquid‐Crystalline Phase in Dilute Aqueous Solutions of Methylcellulose

Summary: The existence of liquid‐crystalline (LC) phases in dilute methylcellulose solutions is demonstrated by exothermic peaks in differential scanning calorimetry (DSC) curves upon heating and is evidenced by a discontinuity of the dynamic storage modulus when the concentration of methylcellulose increases. This crystalline phenomenon is further confirmed by polarized light microscopy and optical rotatory dispersion measurements. It is found that the appearance of the LC formation is related to the temperature, concentration, and molecular weight of methylcellulose.

The exothermic peaks in DSC curves upon heating and cooling, and conformational transitions in ORD profiles for 2.5 g · L⁻¹ SM4000 methylcellulose aqueous solutions.