一种阻燃抗静电聚丙烯的流变性能

采用毛细管流变仪和旋转流变仪分别研究了溴系阻燃剂、炭黑填充对聚丙烯熔体高剪切挤出畸变和动态黏弹特性的影响。发现低含量下随填充量的提高,发生挤出畸变的临界剪切速率提高,扩大了加工窗口。动态流变试验表明树脂中添加更多炭黑后剪切变稀时的复数黏度、储能模量和损耗模量都增大,但损耗因子下降。进一步用缠结模型和Cross模型定量分析表明,填料吸附高分子链段而减少其壁面吸附,减轻挤出畸变,进而提高临界剪切速率;粒子分布网络提高了平台模量和缠结密度,缩短了松弛时间,恢复更快而减小挤出胀大比。复合材料中添加3.5%(质量)炭黑后形成逾渗网络,表现为高零切黏度和长松弛时间,发生"类液-类固"转变;同时材料表面电阻下降明显,此时黏弹逾渗点与导电逾渗点基本一致。     

聚(3-羟基丁酸酯-co-4-羟基丁酸酯)的扩链改性

采用环氧丙烯酸型扩链剂改性聚(3-羟基丁酸酯-co-4-羟基丁酸酯)[P(3HB-co-4HB)],考察了扩链剂对熔体黏弹性、力学性能和成型发泡的影响.用流变仪测试熔体稳态黏度与剪切速率、动态黏弹模量与角频率、模量与时间的关系,用扫描电子显微镜观察改性前后P(3HB-co-4HB)的断面形貌.结果表明,扩链剂的加入提高...     

停放温度对白炭黑填充胶中填料分散及加工流变性的影响

用毛细管流变仪、旋转流变仪、哈普转矩流变仪、透射电镜等手段研究了停放温度对白炭黑填充溶聚丁苯橡胶(SSBR)/顺丁橡胶(BR)混炼胶门尼黏度、剪切黏度、入口压力降和Garvey口模挤出等流变行为和填料分散的影响。结果表明,随着停放温度升高,白炭黑在基体胶中的絮凝程度增加,分散性变差;混炼胶的门尼黏度、剪切黏度和入口压力降升高;停放温度越高,挤出物的外观越差。     

长支链型高熔体强度聚丙烯流变性能的研究——剪切流变

通过辐照法制备了长支链型高熔体强度聚丙烯（LCB-HMSPP），采用高级流变扩展系统（ARES）表征了其熔体黏弹性，采用毛细管流变仪研究了其在高剪切速率下的流变行为。讨论了敏化剂用量、超高相对分子质量聚乙烯（PE-UHMW）对PP熔体黏弹性、流动曲线和黏流活化能的影响。动态剪切流变数据表明，辐照改性制备的LCBHMSPP具有较好的熔体黏弹性，并且其熔体弹性随敏化剂用量的增加而增强，表现在低频端剪切储能模量明显提高，内耗正切变小，零切黏度增大，特征松弛时间变长；辐照过程中添加极少量PE-UHMW也可提高PP的熔体黏弹性。静态毛细管剪切流变测试表明，线形PP和长支链PP的流动曲线较相似，LCB-HMSPP的黏流活化能较线形PP有显著提高，其剪切黏度具有较高的温度敏感性。     

超高分子量聚乙烯凝胶的流变行为

采用旋转流变仪研究了超高分子量聚乙烯(UHMWPE)凝胶的流变行为。通过动态应变扫描测定了UHMWPE凝胶的线性黏弹区;通过动态温度扫描、动态频率扫描和稳态速率扫描研究了温度、浓度、剪切速率对凝胶流变行为的影响。结果表明,浓度为2%~22%的UHMWPE凝胶的线性黏弹区对应的应变下限为2%,上限为40%,且温度对凝胶线性黏弹区的影响较大;浓度为6%的UHMWPE凝胶,在180℃时,弹性模量最大,凝胶内部的黏结性最强;UHMWPE凝胶熔体的黏度随扫描频率、剪切速率的升高而降低,呈现明显的剪切变稀行为,属于假塑性流体;剪切速率较高时,UHMWPE凝胶的黏度对温度的变化更敏感。     

聚烯烃弹性体的结构与熔体黏度关系的研究

采用凝胶渗透色谱仪和核磁共振仪表征了一系列聚烯烃弹性体（POE）样品的结构,并用毛细管流变仪考察了其挤出稳定性、剪切依赖性和黏温依赖性,分析了熔体黏度与聚合物结构的关系。结果表明,随着剪切速率的提高,高相对分子质量的POE熔体易出现不稳定流动,挤出物表面发生畸变;相对分子质量越大、温度越低、共聚单体含越高,发生不稳定流动的临界剪切速率c越低;POE的剪切黏度很大程度上受相对分子质量的影响,与共聚单体的含量关系不大;不同相对分子质量及组成的POE熔体的黏流活化能相近,约为2.8×10^4 J/mol。基于Carreau、Cross和Arrhenius等方程,分别建立了关联熔体零切黏度与聚合物重均相对分子质量和温度关系的半经验式、关联熔体表观黏度与零切黏度和剪切速率关系的半经验式;两式可用于预测POE熔体的黏度,其适用范围为温度为130~190 ℃,剪切速率为10~2 000 s-1,重均相对分子质量（Mw）为4.2×10^4~1.24×10^5 g/mol。     

适于微成型加工的聚乳酸/聚甲醛共混物流变行为研究

将聚甲醛(POM)与聚乳酸(PLA)熔融共混,制备了PLA/POM复合材料。POM的引入明显改善了PLA的熔融加工性能,有利于PLA微成型加工。采用熔体流动速率仪、高压毛细管流变仪和动态流变仪研究了PLA、POM及PLA/POM共混物的流变行为。结果表明:随着POM含量的增加,PLA/POM共混物的熔体流动速率亦增加;PLA、POM和PLA/POM共混物熔体具有假塑性流动特征,是非牛顿流体。随POM含量的增加,PLA/POM共混体系的剪切黏度降低,且剪切敏感指数减小,非牛顿指数升高。PLA、POM及PLA/POM共混物都具有类黏弹性,其黏弹行为均以黏性为主。此外,相对PLA,POM的加入降低了PLA/POM共混体系的复数黏度、动态储能模量和动态损耗模量,但提高了力学损耗。     

淮山药黏液稳定性与黏弹响应的关系

研究了淮山药黏液稳定性与黏弹响应的关系,发现在测试频率范围内,储能模量(G)始终大于损耗模量(G″),且均随频率变化不大,呈现出较强的网络结构特征,黏液性质对频率不敏感。黏液的表观黏度(a)与剪切速率(■)的关系可用Carreau模型较好地拟合,增大,黏液发生剪切变稀现象,表明黏液性质对剪切速率的变化较敏感;黏液的增比黏度(ηsp)与浓度(c)的关系为ηsp∝c3.01±0.12,黏液处于亚浓缠结区域。此外,盐度对黏液的黏弹响应影响较大,盐度增加,蛋白质分子间的静电排斥作用被屏蔽,分子间缠结增强,黏液的储能模量、损耗模量以及复数黏度(η*)逐渐上升,对黏液稳定性有一定影响。     

聚烯烃熔体两类挤出畸变现象的定量描述

采用恒速型双毛细管流变仪研究一批聚烯烃熔体的高速挤出行为.定义了定量描述两类挤出畸变现象--鲨鱼皮畸变和挤出压力振荡的若干物理参数.定量描述了温度、挤出速率、熔体材质及成分对挤出压力振荡和鲨鱼皮畸变的影响规律.发现线型聚合物熔体高速挤出时易发生鲨鱼皮畸变和挤出压力振荡,而支化聚合物或主链含大侧基聚合物熔体很少出现同类畸变.挤出速率增大,压力振荡的频率加大,振荡加剧;挤出温度升高,开始发生振荡的临界剪切速率增高,熔体流动不稳定性减轻;但对同一熔体而言,不同温度下开始发生压力振荡的临界剪切应力变化不大.     

含炭黑PET的流变性能研究

采用毛细管流变仪对含炭黑聚对苯二甲酸乙二醇酯(PET)切片的流变性能进行研究,并与普通PET切片的流变性能进行比较。结果表明:在一定的测试温度下,含炭黑PET熔体为剪切变稀的假塑性非牛顿流体;随温度的升高,含炭黑PET熔体的表观黏度逐渐下降,非牛顿指数逐渐增大;含炭黑PET熔体的黏流活化能随剪切速率的增大而逐渐减小;在含炭黑PET的纺丝过程中,可以通过升高温度、提高剪切速率来改善熔体的流动性能。     

A study of rheological behavior of a polypyrrole modified UHMWPE gel using a parallel plate rheometer

Polypyrrole powder was added to a 6% UHMWPE decalin solution as an interfacial modifier. Rheological properties and dynamic viscoelastic properties, including shear viscosity, shear storage modulus (G′), and shear loss modulus (G″), were measured with a parallel plate rheometer using rotation and oscillation modes. The results show that these properties increase with the PPy content. In addition, the gelation temperature decreased with increasing PPy content. This suggests that the presence of PPy enhanced the entanglement network in the solution, which is similar to the role of filler in rubber.     

A study of melt density of flowing linear polyethylene

Linear polyethylene was extruded from a capillary rheometer with the driving piston operated at fixed speed and at fixed pressure. Apparent viscosity and melt density were measured in both extrusion modes. Apparent density decreased at shear rates approaching the melt fracture region in fixed piston-speed operation. Flow of other polymer melts was essentially incompressible in fixed piston-speed operation, and all polymers exhibited incompressible flow in fixed-pressure extrusion. The oscillating portion of the flow curve of linear polyethylene reflects alternating periods in which the polymer exits faster and slower than the rate at which the advancing piston clears the rheometer reservoir. Linear polyethylene behaves differently from most other polymers in fixed piston-speed extrusion and during melt fracture because of the existence of a more extensive entanglement network in the melt. It is suggested that melt fracture in general results from a tensile failure of the entanglement network, which may occur at the die inlet and in the orifice.     

Study on the viscosity of polypropylene composites filled with different size and size distribution CaCO3

Two kinds of different size calcium carbonates are blended and filled into polypropylene in 30 wt%. The melting viscosity of PP composites samples is measured by capillary extrusion rheometer at 230°C. The results show that the melt viscosity of PP composites evidently decreased when that was filled with the blending 325 and 1,500 mesh CaCO₃ and the 1,500 mesh proportion in fillers was from 20 to 60 wt%. The viscosity in the low shear velocity decreased more than that in the high shear velocity. The shear viscosity of single filler and filler samples with the size distribution at the different temperature was studied by capillary extrusion rheometer. The results show that the flow activation energy and the flow activation entropy of composites filled with the size distribution filler increased. The change of the flow activation entropy and the model of the efficient arrangement of the structure are used to explain the phenomenon in melting viscosity decrease of PP filled with the size distribution fillers. A structural model of composites that filled with the size distribution fillers was set up. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

热氧老化对长玻璃纤维增强PP材料动态流变性能影响

通过熔融共混法制备长玻璃纤维增强聚丙烯(LGFPP)复合材料,采用旋转流变仪和扫描电子显微镜测试研究了不同热氧老化时间下复合材料的动态流变行为。结果表明,热氧老化过程PP发生降解,分子量降低,同时随老化程度的加深分子链的缠结以及分子间相互作用力逐渐被削弱,分子链松弛能力增加;树脂的降解过程容易在纤维与基体的界面区域进行,使得纤维与基体的界面性能下降,粘结力下降。因此,随老化时间的增加复合材料的储能模量、损耗模量、损耗因子以及复数黏度都呈现下降趋势。     

Effects of wall slip on the rheological measurement and extrusion die design of a filled rubber compound

We investigate the rheological properties of a filler-reinforced rubber compound using a rotorless shear rheometer specially designed for rubber and a rotational rheometer with parallel-plate geometry. Our aim is to evaluate the effects of wall slip on both the oscillatory and steady shear modes of the rotational rheometer. The rheological measurements show that the slip generally does not affect the oscillatory shear but does exist in the steady shear flow and tends to make the measured shear viscosity lower than the true value. Besides, we extend the investigation into engineering applications. The extrusion die for a given extrudate profile is obtained using a finite-element model in which the wall slip is considered as a boundary condition. To validate the die design, an extrusion experiment is carried out and the results confirm that, for filled elastomers, it is necessary to consider the effect of wall slip in the extrusion die design.     

Rheological behavior and network dynamics of silica filled vinyl‐terminated polydimethylsiloxane suspensions

Present article reports the rheological properties and network dynamics of fumed silica filled vinyl‐terminated polydimethylsiloxane suspensions. The results reveal that as filler loading increases, the span of the linear viscoelastic region with constant dynamic storage modulus is narrowed with increase in strain amplitude while the relaxation time of the compounds get shifted to longer time scales. The dynamics of filler‐network indicated significant Payne effect due to fumed silica incorporation into the PDMS matrix. Further, strain‐induced agglomeration of fumed silica particles, characterized by a peak in the dynamic loss modulus curve could also be observed. High loss‐tangent was observed for lower contents of filler in the suspension, an effect with an apparent relationship to the loosely formed filler‐network. The formation of a saturated network structure of fumed silica particles was evident from the dynamic modulus and complex viscosity data, that remained unaffected with frequency till a critical amount of fumed silica loading. Han plots (storage modulus versus loss modulus) revealed the microstructural changes for various filled systems that was attributed to build‐up of the filler‐network causing an apparent evolution of yielding phenomenon. Van Gurp‐Palmen plots (complex modulus versus phase lag) showed that flow behavior of the filled PDMS suspensions resembled to that of typical viscous fluids. POLYM. ENG. SCI., 57:973–981, 2017. © 2016 Society of Plastics Engineers     

Rheological behaviour of polystyrene latex near the maximum packing fraction of particles

Additional developments in the comprehension of the rheological behaviour of polymer latices, especially near the high critical concentration ?_c, are presented for two polystyrene latices of average particle diameters close to 200 nm with different electrostatic properties. Not surprisingly, there is a rapid transition in the rheological characteristics over a narrow range of polymer volume fractions as the concentration of the disperse phase increases. By examining twelve different polymer volume fractions a unique value of the critical volume concentration, ?_c, was found for each latex. At this point, the steady shear viscosity, dynamic modulus, and dynamic shear viscosity change dramatically. Furthermore, these critical concentrations are well confirmed by the percolation theory for the dynamic zero shear viscosity as a function of volume fraction. The Cox-Merz rule is not obeyed by these dispersions at the concentrations greater than ?_c. By using a controlled strain Couette rheometer with a gap of 1.2 mm, shear thickening limits were also observed for both latices. The concentration dependence of the onset shear rate for shear thickening changes near ?_c for each of the two latices.     

PA6/MMT/SGF复合材料的流变性能

利用毛细管流变仪和动态流变仪分别测试了纯尼龙(PA)6以及PA6/蒙脱土(MMT)和PA6/MMT/短玻璃纤维(SGF)复合材料的剪切粘度、复数粘度、储能模量和损耗模量,并用Han曲线分析了材料的粘弹特性.结果表明,在低剪切速率下,PA6/MMT和PA6/MMT/SGF复合材料的剪切粘度大于纯PA6的剪切粘度;在高剪切速率下,PA6/MMT和PA6/MMT/SGF复合材料剪切粘度低于纯PA6的剪切粘度.动态流变测试显示,PA6/MMT/SGF复合材料在低频区呈类固响应,其储能模量和复数粘度明显提高.Han曲线表明,PA6/MMT/SGF复合材料的粘性响应占主导地位.     

Shear viscosity of carbon black filled polypropylene at very low shear stresses

The shear viscosity of carbon black filled polypropylene with a range of different carbon blacks was investigated. This was accomplished using (a) a constant shear stress creep instrument, (b) a cone-plate rotational rheometer, (c) a capillary extrusion rheometer. It was found that stresses exist for these compounds below which there are only finite deformations and no steady flow, Much attention was given to measurements of creep at low stresses, especially in the neighborhood of yield values. The magnitudes of yield stresses obtained from such creep measurements are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stress data from rotational instruments. The shear viscosity behavior near the yield value differs significantly depending upon the carbon black used. A high viscosity was observed (～10⁹ to 10¹⁰ Pa.s) plateau in some compounds.     

聚丙烯腈/离子液体溶液流变性能的研究

采用应力流变仪对聚丙烯腈/1-丁基-3-甲基咪唑氯化物(PAN/[BMIM]Cl)溶液体系的稳态和动态流变性能进行了研究,讨论了PAN相对分子质量(Mη)对溶液稳态和动态流变性能的影响。结果表明:PAN/[BMIM]Cl溶液在低剪切速率区表现出牛顿流体特征,在高剪切速率区随着剪切速率的增大粘度降低,表现为切力变稀流体;溶液的粘度大于常规溶剂体系,随着PAN的Mη增大,PAN/[BMIM]Cl溶液表观粘度明显增大,非牛顿指数减小,粘流活化能增大;溶液的损耗模量和储能模量越大,溶液更容易表现出弹性效应。