振动力场下聚合物熔体流变行为的响应与分析 Ⅰ.毛细管压力降和熔体表观粘度

在自行设计的恒速型毛细管动态流变装置上 ,对聚合物熔体进行动态挤出实验。借助已建立的振动力场下聚合物熔体流变行为的表征公式 ,分别计算振动力场下聚合物熔体在毛细管壁处的剪切应力、剪切速率和表观粘度。与稳态挤出时相比 ,引入振动力场后 ,发现毛细管压力降、表观粘度均显著降低 ,且随着振动频率和振幅的改变呈非线性变化趋势 ,作者对此进行了深入分析。     

振动力场下聚合物熔体流变行为的响应与分析——I．毛细管压力降和熔体表观粘度

在自行设计的恒速型毛细管动态流变装置上，对聚合物熔体进行动态挤出实验。借助已建立的振动力场下聚合物熔体流变行为的表征公式，分别计算振动力场下聚合物熔体在毛细管壁处的剪切应力、剪切速率和表观粘度。与稳态挤出时相比，引入振动力场后，发现毛细管压力降、表观粘度均显著降低，且随着振动频率和振幅的改变呈非线性变化趋势，作者对此进行了深入分析。     

振动力场下螺旋芯棒式管材机头内熔体流动的数值模拟

为了研究振动力场作用下螺旋芯棒式管材机头内熔体的流动特性,考虑非定常流动,使用Polyflow软件首次对熔体的流场进行了全三维非牛顿等温数值模拟。研究表明,随着振动力场的引入,流道内熔体的剪切速率、黏度、剪切应力、压力和速度等呈周期性规律变化。另一方面,随着振动频率或振幅的增加,流场的剪切速率平均值增加,而流场的黏度平均值、剪切应力平均值和压力平均值下降。     

聚合物熔体缝模内脉动挤出过程的研究

研究了振动场作用下聚合物熔体通过狭缝型流道的脉动挤出过程,探讨了振动参数与聚合物熔体铗缝流的压力降和流率之间的相互关系。结果表明,随着振动场频率和振幅的增加,聚合物熔体狭缝流的压力降减小,流量增率增大。     

振动注射成型中模腔冷却过程的研究

研究了振动注射成型中模腔内聚合物溶体产生的振动剪切热,并研究在振动作用下模腔内物料的冷却过程。结果表明,模腔内熔体的温升速率随着振动频率、应变振幅及振动剪切速率的增加而增加,随熔体温度的增加而减少。由于振动剪切换,使振动注射成型需要更长的冷却时间。     

振动剪切作用下聚合物熔体的非仿射网络结构模型——振动参数对聚合物熔体弹性的影响

利用非仿射瞬态网络结构本构模型来分析正弦脉动流场中的聚合物熔体第一、第二法向应力差系数的变化规律，以及振动参数(振动频率和振幅)对聚合物熔体的影响作用。结果表明，在实际加工中可以通过增加振幅或振动频率来降低聚合物熔体的弹性，此模型还可以预测到最佳振幅或最佳振动频率。     

振动注射成型中模腔内熔体冷却行为的研究

研究了振动注射成型过程中的模腔内聚合物熔体的冷却行为,讨论了振动频率、振动应变振幅、振动作用时间、熔体温度等对冷却时间的影响。结果表明,冷却时间随着振动频率、振动应变振幅、振动作用时间、熔体温度等的增加而延长。     

聚合物熔体在振动场中的流变行为研究

利用自行研制的振动试验装置研究了振动场中聚合物ＨＤＰＥ、ＰＳ熔体在不同压力、温度、频率、振幅条件下的流变行为。试验结果表明,熔体表观粘度随振动频率的增加而降低,但降低的幅度随压力、温度和振幅的不同而不同。     

聚合物熔体窄缝脉动挤出行为的光散射研究

利用聚合物熔体的双折射性质,对振动力场作用下窄缝挤出模头中的聚合物熔体脉动挤出行为进行光散射研究,用光弹性图像和光强度矩阵来表征聚合物熔体受到的剪切应力。振动力场的引入使光弹性图像和光强度矩阵发生了规律性变化。结果表明,振动力场使聚合物熔体剪切应力减小、表观粘度降低,最终使得挤出压力降低、产量提高。     

振动剪切作用下聚合物熔体的非仿射网络结构模型 Ⅱ．非仿射网络结构模型

假设聚合物熔体的缠结网络形变是非仿射的，运用瞬态网络结构原理，采用在本课题第一部分^[1]中所建立的动态速率方程，并对上随体Maxwell本构方程加以修正来建立一个非仿射网络结构模型，利用这一模型来研究振动剪切作用下LDPE熔体的流变行为，研究表明，随着应变振幅和频率的增加，LDPE熔体的剪切应力也增加，同时指出了非仿射网络结构模型的精确变比仿射结构模型有较大提高，这表明在振动力场作用下，网络形变发生了非仿射形变，因此在建立振动力场作用下聚烯烃熔体本构方程时，不能假设其网络是仿射形变的。     

聚乳酸／蒙脱土纳米复合材料的流变行为

采用熔融插层法制备了插层型的聚乳酸／蒙脱土纳米复合材料，利用旋转流变仪对其流变行为进行了研究。稳态预剪切和大振幅振荡剪切实验结果表明，蒙脱土晶粒逾渗网络结构具有剪切敏感性，但稳态预剪切更容易破坏蒙脱土晶粒的逾渗结构；反向流和起始流实验结果表明，剪切破坏的逾渗网络在静态退火过程中可以重建，而应力过冲现象的出现则是网络重建的标志；不同剪切速率下应力过冲的最大值都出现在2％应变处，这种应力与应变之间的标度关系表明蒙脱土晶粒类液晶态的形成可能是网络重建的驱动力。     

高分子材料动态成型过程中熔体非线性行为的研究

借助流变测量和连续介质理论,不依赖已有的本构关系,对平行叠加正弦振动条件下高分子熔体经毛细管的动态挤出过程进行了理论分析。以低密度聚乙烯(LDPE)为原材料,实验测量LDPE熔体在一定振动频率和振幅下毛细管入口压力、体积流量和挤出胀大的瞬态值,即可得到动态成型过程中高分子熔体剪切应力、剪切速率和表观粘度的变化规律:随振幅和频率的变化,LDPE熔体的表观粘度呈非线性变化趋势;在不同的振幅和频率下动态挤出LDPE熔体,跟稳态挤出时一样,壁面剪切应力与壁面剪切速率也成非线性比例关系。     

Shear-induced interactions in blends of HMMPE containing a small amount of thermotropic copolyester HBA/HQ/SA

Shear-induced interactions between high molecular mass polyethylene (HMMPE) melt and a thermotropic liquid crystalline copolyester, HBA/HQ/SA (TLCP) were investigated using large amplitude oscillatory shear and capillary shear. Polarized optical microscopy (POM) observations show that the mono-domain nematic TLCP droplets embedded inside a HMMPE melt may be readily elongated using large amplitude oscillatory shear. The HMMPE melt adjacent to the elongated TLCP filament was observed to crystallize faster than that in the matrix away from the interface. TEM analysis on the 1 wt% TLCP/HMMPE blend quenched after capillary shear shows that there are strong interfacial interactions between the elongated TLCP filament and the HMMPE matrix. Long range PE lamellae orientational order up to 2 μm away from the TLCP filament surface were observed, with all the lamellae surface normal parallel to the TLCP fiber. Additionally, a strong interfacial compatibility between the TLCP filament and the HMMPE matrix with an interfacial thickness of ∼30 nm has also been observed. The enhanced interfacial compatibility is attributed to the -CH₂- group interactions due to chain alignment in both components at their interface. These results provide a fundamental insight to other TLCP containing thermoplastics where compatibilities may be present due to segmental interactions.     

Polarization-optical investigation of polymers in fluid and high-elastic states under oscillatory deformation

The relationship was investigated between birefringence and oscillatory shear deformation of linear high molecular mass polymers exemplified by narrow- and broad-distribution polybutadienes and polyisoprenes. Polymer deformation at different frequencies and amplitudes was carried out in an annular gap. The stress field uniformity was not below 95%. It was shown that in oscillatory deformation of polymers in the fluid and high-elastic states, birefringence contains a time-independent steady component and an oscillatory component with a frequency equal to that of the assigned oscillation. A linear interrelation was found to exist between the amplitude of the oscillatory component of birefringence and that of the shear stresses, with a proportionality factor equal to the stress-optical coefficient of the polymers. The phase of the oscillatory component of birefringence coincides with that of the shear stresses. Measurements of the steady component of the birefringence make it possible to find the steady component of the first normal stress difference resulting from the assignment of shear oscillations to the polymer. On the basis of the experimental data obtained for polybutadienes and polyisoprenes, and the literature data for polystyrene solutions, a master curve was constructed that generalizes the dependence of the steady component of the first normal stress difference in the linear and nonlinear deformation regimes on the product of the square of the deformation amplitude and the storage modulus measured at low amplitudes. This dependence is valid in the linear and nonlinear deformation regimes. It is invariant with frequency, amplitude deformation, molecular mass, and molecular mass distribution of the polymers. It is shown by visual observation of deformation that the abrupt drop in resistance of polymer to shear in large-amplitude deformation is due to polymer rupture near the surface of the inner cylinder and is accompanied by a slip-stick process. This is the phenomenon of spurt early observed in capillary viscometers at high shear stresses and recently investigated in coaxial cylinder devices at large amplitude deformation.     

Thermo-rheological analysis of various chain extended recycled poly(ethylene terephthalate)

Three chain extenders, pyromellitic dianhydride (PMDA), ethylene carbonate (EC), and a polymeric-epoxide, were investigated for improving recycled p(ethylene terephthalate) (r-PET) properties with melt extrusion. The amount of additives and processing temperatures were also varied to check for melt degradation. Small amplitude oscillatory shear experiments were performed to probe rheological changes with different chain extenders. Capillary rheometry with haul-off was also performed to measure extensional viscosity and melt strength. Higher loadings of the chain extenders were found to improve properties of r-PET. These chain extenders definitely increased melt viscosities when incorporated at the higher level of the ranges examined, matching that of virgin PET. EC addition resulted in high shear thinning of the polymer. Epoxy and PMDA added to r-PET produced products with the same extensional viscosity as v-PET. Haul-off experiments demonstrate superior performance by epoxy-modified r-PET compared to v-PET.     

Harmonic Analysis of a Solder Paste under Large Amplitude Oscillatory Shear

Large amplitude oscillatory shear experiments, as an alternative measurement technique for nonlinear rheology, were performed using a cone‐plate rheometer with a solder paste. We found that odd harmonics appear in the stress waveform. A two‐segment, piecewise linear model was introduced to analyze the experimental observation. The procedure for calculating the crossover shear rate, the first and second region viscosity, and an apparent yield stress from harmonic amplitude data are shown. This technique observes a time‐dependent structural transition between the unsteady initial state and the secondary state. We found that the crossover time depends on shear rate amplitude and can be represented in the quadratic form of imposed shear rate.     

振动力场下聚合物熔体缠结密度理论研究

本文对Liu(1981)提出的动态速率方程加以修正 ,用修正的速率方程来研究振动剪切场下缠结密度的变化情况 ,指出当施加正统应变后 ,缠结密度的变化也呈周期性变化 ,而且施加的应变振幅与频率的大小对缠结密度的变化有很大影响 ,当施加的应变振幅或频率越大时 ,缠结密度变化的幅度越大 ,从而使熔体的粘度变化也越大。同时指出施加振动可以减少链段和整个分子链的松弛时间 ,而且初始平衡态时的平均缠结点数越少 ,施加振动后的缠结密度变化幅度越大     

Rheology of wood plastics melt,part 3: Nonlinear nature of the flow

The nonlinear rheology of HDPE/maple melt in both shear and extensional flow was studied using a rotational parallel plate rheometer and the hyperbolic die technique, respectively. Nonlinear features were found in oscillatory shear tests at strain levels far below the values for neat polymer melt. The shear stress relaxation tests revealed the time–strain factorizability, and the damping function was found to follow the sigmoidal‐type relation. The nonlinear nature of the shear flow was further observed as the shear stress growth function from step rate tests as compared to the prediction based on linear viscoelasticity. Extensional stress growth functions of the filled HDPE was build through the viscosity data based on hyperbolic dies with different Hencky strain. The comparison with prediction based on linear viscoelasticity and the Trouton's law further indicated significant damping owing to the particulate suspension nature of the wood plastics melts. POLYM. ENG. SCI., 46:114–121, 2006. © 2005 Society of Plastics Engineers