剪切对泡沫夹层结构梁弯曲性能的影响

本文以受剪后横截面仍为一平面但与轴线不再垂直为基本假设,采用能量法建立了一种对泡沫夹层结构梁的弯曲性能进行分析的方法。通过对比试验数据以及有限元的计算结果,得到用该方法可较为准确地预测泡沫夹层结构梁的挠度。通过分析,得到了剪切对泡沫夹层结构梁挠度的影响程度随着梁的跨高比的增大而减小,同时讨论了梁横截面正应变及正应力的分布情况。     

The failure behavior of a polyurethane composite coating in 3.5% NaCl solution under ultraviolet irradiation

The failure process of inorganic zinc‐rich/micaceous iron oxide epoxy/aliphatic polyurethane composite coating in 3.5% NaCl solution under ultraviolet irradiation (UV) was studied with electrochemical impedance spectroscopy (EIS) and Fourier transform infrared (FTIR) spectroscopy. UV irradiation significantly accelerated failure process of the composite coating in NaCl solution. The effect of UV on failure process of the coating system in 3.5% NaCl solution may be divided into two stages: in the early stage, the thermal effect generated by the ultraviolet irradiation is the main reason leading to the increase in coating porosity, but this effect is not serious and the coating remains high impedance and good protection ability. In the latter stage, the fracture of polymer chains in the top coating by UV irradiation is the main factor resulting in quick decrease of coating performance. C N and C O bonds in polyurethane coating are broken by UV irradiation, leading to quick increase of the coating porosity and decrease of the coating resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of small rubber particles on the environmental stress cracking of high impact polystyrene

This article exploits the influence of rubber particle size (RPS) and rubber crosslinking on environmental stress cracking resistance (ESCR) of high impact polystyrene (HIPS), with special interest on the influence of small rubber particles fraction. Three commercial HIPS of high ESCR were selected and four batches of HIPS were prepared in‐house, including samples based on high cis and very high viscosity polybutadiene (PB). Their morphologies were analyzed by low angle laser light scattering, optical microscopy, and transmission electron microscopy, and the samples were submitted to flexural ESCR tests with fatty agents. The ESCR to sunflower oil was found to increase with the reduction of the rubber particles fraction smaller than 1–2 micron. Results have also confirmed that an increase in RPS is the key parameter to promote ESCR, although there is limit for RPS to be effective on ESCR improvement. The reduction of small rubber particles fraction in HIPS was achieved by using a high cis PB, that promotes low grafting efficiency of polystyrene onto PB backbone because of the low content of 1,2 vinyl isomer. Besides the ESCR improvements, HIPS with high cis PB showed higher elastic modulus and impact resistance than HIPS containing medium cis PB, which is desired for thickness reduction in food packaging and refrigeration cabinets. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental Studies on Suspension of Solid Particles in a Low‐Shear Stirred Vessel

A low‐shear stirred vessel was explored. Experimental studies on the suspension of solid particles in solid‐liquid and gas‐solid‐liquid systems were conducted to examine the performance of this new reactor. The method based on the power number curve was modified to determine the critical impeller speeds required for just complete off‐bottom suspension of solids under non‐gassed (N_js) and gassed conditions (N_jsg) in this reactor, and a PC‐6A fiber‐optic probe for the measurement of solid distribution was used to complementarily validate this method. A more homogeneous flow field was gained with a draft tube installed, so that the standard deviations of average shear rate and maximal shear rate are reduced. The modified power consumption method can determine N_js and N_jsg, and the values of N_js with a draft tube are much lower than those without it. N_jsg increases slightly with increasing gas flow rate, and N_jsg with a higher solid weight fraction is larger in this lower‐shear reactor.     

垂直管内弹状气泡上升中壁面传递的实验研究

垂直管内弹状流壁面传递是诸多工业应用中需研究的重要问题之一。今用极限扩散电流技术,对弹状气泡上升时瞬时壁面剪应力和传质系数进行了测定,结果显示:当基于表观气速的Froude数FrG < 0.74时,壁面剪应力随弹状气泡和液塞的到来呈现方向相反的交替变化,壁面传质系数亦相应变化;而当FrG > 0.74时,剪应力方向一直向下,说明液膜向下流动,且弹状气泡和液塞的到来对壁面传质系数的影响很小。这说明下落液膜射流穿透了液塞段,控制了整个壁面传递过程。研究还对下落液膜区、尾迹区及液塞段的不同传递特征及机理进行了分析, 并结合气泡塔熔融结晶器中弹状气泡上升时的传热,对结晶操作条件的合理选择进行了讨论。     

蔗渣浆低浓黑液多聚物粘度对温度依赖性的关联模型

利用聚合物自由体积理论模拟了蔗渣浆低浓黑液对粘度对温度的依赖性的数学模型，最终得出黑液多聚物粘度与温度的相关式：η=A1exp[B1/(T-T0)]。利用示差扫描量热分析技术（DSC）得出了蔗渣黑液多聚物中连续相与分散相的转变曲线，并获得了表观温度T0的平均值为255K；通过实验数据拟合可回归出蔗渣黑液多聚物在不同浓度时的系数A1和B1值。因此，使用该粘度的数学模型可估算蔗渣低浓（接近40％固含量）黑液多聚物在操作温度范围内（20－100℃）的粘度值。     

Effect of processing conditions on the yield and failure response of an aliphatic polyketone terpolymer

The effect of processing conditions on the yield and failure behavior of an aliphatic polyketone terpolymer was studied. Testing and characterization were performed on samples that were extruded in the form of hollow cylinders. We performed the extrusion process at different shear rates and at different cooling rates to assess the effect that process conditions had on the polymer properties. We performed biaxial testing on the samples to characterize the failure envelopes, including the ductile–brittle transition condition for each process condition. The effect of shear rate was negligible, whereas the cooling rate significantly affected the failure behavior. To explain these differences in behavior, we performed characterization via differential scanning calorimetry, wide‐angle X‐ray diffraction, attenuated total reflection IR spectroscopy, dynamic mechanical thermal analysis, scanning electron microscopy, and residual stress measurements. A broad glass transition was found for all samples at temperatures higher than previously reported for this material. Alteration of the processing conditions did not influence the crystalline phase (percentage crystallinity, crystalline orientation, crystallite size, etc.). A change in spherulitic structure was also observed with altered cooling rate and is suggested to have contributed to the change in failure behavior. Residual stresses also affected the behavior of all samples. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 318–334, 2002; DOI 10.1002/app.10334     

Recoverable shear strain of liquid crystal‐forming concentrated hydroxypropyl cellulose solutions

The recoverable shear strain (S_R) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. S_R greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of S_R on stress and concentration. S_R increased with increasing stress for the single phase and decreased for the biphase. S_R seemed to be related to the die swell (B): S_R ∝ Bⁿ. S_R exhibited a maximum and a minimum with respect to concentration. S_R for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater S_R. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002     

Friction of linerboard based on recycled fiber

The purpose of this investigation was to study the origin of the differences in paper‐to‐paper friction of linerboards based on old corrugated containers (OCC). The sheets were subjected to two extraction stages and analyzed with respect to, surface roughness, and their content of low‐molecular‐mass lipophilic compounds (LLC). Friction was measured using a friction tester based on the horizontal plane principle. The surface roughness was measured using a Perthometer profiler and the low molecular mass lipophilic constituent of the paper sheets was determined by gas chromatography‐mass spectroscopy. The sheets were imaged using environmental scanning electron microscopy (ESEM), and the relative compositions of inorganic ions on the paper surfaces were determined by energy dispersive X‐ray spectroscopy (EDS). The results showed that a high amount of LLC in the sheets lead to low friction, due to lubrication. It was also observed that large CaCO₃ particles on the surface had a friction‐increasing effect, and that there was no relationship between the surface roughness and the friction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1511–1520, 2002     

Comparison of relative viscosity measurement of polyvinylpyrrolidone in water by glass capillary viscometer and differential dual‐capillary viscometer

The relative viscosity (RV) of polyvinylpyrrolidone (PVP) with different molecular weights was measured with a glass capillary viscometer and with a differential dual‐capillary viscometer in water at different concentrations. For the differential dual‐capillary viscometer, RV increases with a decreasing flow rate, especially for high molecular weight PVP at a 1% concentration. A good agreement in the RV between the two methods can be obtained for PVP with different molecular weights and at various concentrations if an appropriate flow rate is selected for the differential dual‐capillary viscometer. Special precaution is needed when using the differential dual‐capillary viscometer to measure the viscosity of a pure solvent. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1312–1315, 2002