熔体拉伸PE–HD和PE–LLD薄膜的制备及性能

以高密度聚乙烯(PE–HD)和线型低密度聚乙烯(PE–LLD)树脂为原料,采用转矩流变仪,借助熔体拉伸法制备了具有取向结构的PE–HD膜和PE–LLD膜。利用偏光显微镜、傅立叶变换红外光谱、差示扫描量热、小角激光散射及力学性能测试分析不同熔体拉伸速率下PE–HD膜和PE–LLD膜的结构与性能变化情况。结果表明,熔体拉伸速率越高,PE–HD膜和PE–LLD膜的相对取向度越高,快速拉伸PE–HD膜和PE–LLD膜的相对取向度分别为2.043和1.556;熔体拉伸速率对PE–HD膜和PE–LLD膜的结晶温度影响不大,两种膜具有显著的结晶性,PE–HD膜的结晶性更好;随熔体拉伸速率的提高,PE–HD膜和PE–LLD膜的拉伸屈服应力和拉伸弹性模量提高,断裂伸长率降低,总体上看,PE–LLD膜的断裂伸长率较PE–HD膜高,而拉伸强度较PE–HD膜低。     

PP／PE-HD共混体系在压力振动注射成型中的形态与性能研究

探讨了采用自行研制的压力振动注射成型装置对加工聚丙烯（PP）/高密度聚乙烯（PE—H19）共混物的影响。结果表明：两相相容性得到一定改善，试样的力学性能得到了大幅度的提高，其中PP／PE—HD（60／40）组分的冲击强度相对于普通注射提高了约294％。示差扫描量热测试表明振动注射会使PP和PE—HD具有部分的相容性，且样品结晶度比常规注射的高。广角X射线衍射分析表明振动注射成型有利于y晶的生成，从而试样的模量及强度得到提高。扫描电镜测试表明采用振动注射成型后，PE—HD分散相的尺寸明显变小而且分布更加均匀，实现了两组分之间的微区分离。     

界面对PE–LLD/Al（OH）3复合材料性能影响

制备了丙烯酸(AA)接枝线型低密度聚乙烯(PE–LLD)(PE–g–AA)高分子偶联剂,并将其用于改性PE–LLD/Al(OH)3复合材料。研究了PE–g–AA对PE–LLD/Al(OH)3复合材料的微观结构、力学性能、流变行为、电气绝缘性能的影响,并探讨了复合材料力学性能、电气绝缘性能和界面微观结构之间的关系。研究结果表明,PE–g–AA偶联剂显著改善了Al(OH)3填料与PE–LLD基体之间的界面作用机制,不但提高了复合材料的拉伸和冲击强度,而且增加了复合材料的断裂伸长率。另外,PE–g–AA提高了Al(OH)3在聚合物基体的分散性并作为绝缘层减少了填料之间的相互接触,因而获得的复合材料的电气绝缘性能在低偶联剂的掺量下大幅提升,达到电气绝缘性能要求。     

硅烷交联POE/PE–LLD软管材料的制备

通过硅烷交联两步法,利用反应挤出原理在单螺杆挤出机上进行硅烷交联乙烯–辛烯共聚物(POE)/线型低密度PE(PE–LLD)软管材料的制备;重点考察了POE用量、硅烷偶联剂种类、引发剂用量及交联时间等对POE/PE–LLD凝胶率、拉伸强度的影响,制得了性能优良的软管材料。研究表明,当POE/PE–LLD质量比为50/50,硅烷偶联剂A151、引发剂过氧化二异丙苯、催化剂二月桂酸二丁基锡用量分别为3%,0.05%,0.5%,交联时间为12 h时,材料的凝胶率达69.4%,拉伸强度达22.8 MPa,耐老化处理后材料的拉伸强度保持率为94%,可应用于耐高温、耐老化软管的生产。     

共聚聚丙烯／茂金属线形低密度聚乙烯共混体系的流变行为与结晶行为

用毛细管流变仪研究了冲击性能相对优良的共聚聚丙烯(cPP)与茂金属低密度聚乙烯(m-PE—LLD)共混物熔体的流变行为。讨论了共混物的组成、剪切应力和剪切速率对熔体流变行为、熔体粘度的影响。测定了不同cPP及m—PE—LLD配比的共混物熔体的非牛顿指数。结果表明：共混物熔体属假塑性流体，但其粘度随m—PE—LLD加入量的增加变化不大。DSC分析及微观形态分析表明，m-PE—LLD的加入使cPP的结晶温度提高，具有异相成核作用。m-PE—LLD对cPP有明显的增韧作用，当m—PE—LLD含量为15％时，共混物的冲击强度明显提高，增幅在75％左右，而拉伸强度保持率为85％以上。     

振动强化锥面磨盘拉伸流动及混合性能模拟

基于拉伸流动原理设计的锥面磨盘可改变流道内熔体流动类型,增大拉伸流场作用。而叠加适当振动参数的振动力场可以进一步增强锥面磨盘流场的拉伸作用、提高拉伸速率,减小分离尺度并使其变化趋稳、增大混合指数并提高混合效率,从而使混合物料粒径减小、粒度均匀,获得良好的混合分散效果,为混合加工设备设计及聚合物混合性能的提高提供了新的参考依据。     

热拉伸过程中PE–UHMW/PE–HD共混纤维的晶体结构演变

将超高分子量聚乙烯(PE–UHMW)与高密度聚乙烯(PE–HD)按照质量比为6︰4进行共混熔融纺丝,并对初生丝进行高倍热拉伸制得PE–UHMW/PE–HD共混纤维。利用广角X射线衍射、差示扫描量热、声速取向试验等方法研究了PE–UHMW/PE–HD共混纤维在热拉伸过程中的晶体结构演变过程。研究显示,随着热拉伸过程的进行,纤维的分子链沿纤维的轴向取向度逐渐增加,熔融峰温度逐渐升高,结晶度逐渐增加;沿径向的晶粒尺寸逐渐减小,而沿轴向的晶粒尺寸逐渐增加,即形成了更细长的晶粒;晶体的取向度逐渐增加。当拉伸倍数由1增大至6时,上述现象变化显著,当拉伸倍数由9增至15时,上述现象变化缓慢。与PE–HD共混后的纤维结晶度、晶体取向度和分子链取向度更高,晶粒更加细长。     

PA6/PE-LLD/EGMA合金的结构与性能研究

以聚乙烯-甲基丙烯酸缩水甘油酯(EGMA)为增容剂,利用反应增容技术制备了聚酰胺6(PA6)∕线性低密度聚乙烯(PE–LLD)/EGMA合金。利用力学性能测试、红外谱图分析和扫描电子显微镜观察等研究了该合金的力学性能、分子结构和微观形态结构。结果表明,EGMA中的环氧基团和PA6端氨基发生了化学反应,且EGMA的乙烯基长链与PE–LLD具有结构相似性,明显改善了PA6和PE–LLD共混两相的界面相容性,PA6/PE–LLD/EGMA合金的力学性能得到了显著提高。     

无卤阻燃PE–LLD复合体系燃烧行为研究

利用锥形量热仪在50 k W/m2热辐射条件下,研究了几种无卤阻燃线性低密度聚乙烯(PE–LLD)体系的燃烧行为。结果表明,PE–LLD/乙烯–乙酸乙烯酯共聚物(EVAC)/改性氢氧化镁/微胶囊红磷体系的阻燃性能最好,其最大热释放速率为182 k W/m2,达到最大热释放速率时间为90 s,燃烧完成时间为1 606 s,最大烟释放速率为0.041 m2/s,最大失重温度时的残炭率为27.7%。该体系在燃烧时使PE–LLD更早的发生热降解,但热降解速度变得缓慢,这与燃烧时炭层的形成密切相关。     

低频振动场对HDPE性能的影响

利用低频熔体振动注射成型技术获得自增强高密度聚乙烯。实验结果表明,采用振动注射成型工艺,试样屈服拉伸强度由26.5MPa提高到36.1MPa;试样的芯层中可获取沿流动方向生成的串晶或行式排列的片晶结构;压力振动注射有利于分子在(110)晶面择优取向,使结晶更加完善;振动注射提高了试样的结晶度,芯层结晶度最大提高了10.2%。     

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

Polyborosiloxane (PBS) was synthesized from boric acid and hydroxyl-terminated polydimethylsiloxane (PDMS). The oscillatory shear behavior of PBS formed by PDMS with different molecular weight was studied. The relaxation time of PBS was calculated by Doi-Edwards model. Finally, the shear-stiffening mechanism of reversibly crosslinked entangled polymer was obtained. Shear stiffening occurs at lower shear frequencies, which is mainly due to crosslinking bonds and friction between molecules hindering the movement of molecules. The increase in storage modulus at high frequencies is attributed to the resistance caused by entanglement in the stretching process of molecular chains. In addition, the molecular weight is greater and the degree of shear stiffening is higher. Such a conclusion is useful to further study the application of shear stiffening. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48421.     

Viscoelastic properties of polystyrene–poly(vinyl methyl ether) blends in oscillatory and steady shear flows near the phase separation temperature

Viscoelastic properties of a polystyrene-poly(vinyl methyl ether) blend were measured in oscillatory and steady shear flows near the phase separation temperature. In the one-phase region, the viscoelastic properties are independent of the type of flow and flow geometry, and their shear and frequency dependences are the same as those of homopolymers. When phase separation occurred, a change in viscoelastic properties was observed in all types of flow and flow geometries, and they are different in the different types of flow and/or different flow geometries in the two-phase region. In the shear rate dependence of viscosity of the polymer blend in the two-phase region at quiescence, a plateau region was observed, in which the shear viscosity can be regarded as the zero shear viscosity of the homogenized polymer blend at that temperature.     

Phase behaviors of diblock copolymer/nanorod composites under oscillatory shear flow

The phase behaviors of lamellar diblock copolymers (DBCPs) melts and lamellar DBCPs/nanorods (NRs) composites subjected to oscillatory shear flow, have been investigated using dissipative particle dynamics. The oscillatory shear is a quite common shearing mode used in experiments and manufacturing processes. The rich lamellar (LAM) reorientation and morphological transition of systems strongly depend on the shear amplitude and shear frequency. At very low frequency, the amplitude‐induced phase behaviors of DBCPs melts or DBCPs/NRs composites are quite similar to those subjected to a steady shear. For DBCPs/NRs case, we control NRs concentration low 15% to preserve LAM morphology in the nanocomposites, and simultaneously consider both types of selective and nonselective NRs. Our aim is to compare the different inductions on DBCPs melts or nanocomposites caused by shear amplitude and frequency, and observe how the NRs are oriented and dispersed in phase‐separated copolymers matrix while under oscillatory shear, and how the presence of selective/nonselective NRs affects the shear‐induced LAM reorientations and rheological properties of systems. Our results show the NRs orientation not only directly depend on the imposed shear flow but also is interfered by the alignment of shear‐stretched copolymer molecules. The shear viscosity decreases with the frequency decreases, also influenced by the NRs concentration and surface property. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

振动剪切作用下聚合物熔体的非仿射网络结构模型 I.动态速率方程

对Liu( 1 981 )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 ,给出其理论分析 ,同时也分析了缠结密度对熔体粘度的影响     

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。     

Large amplitude oscillatory shear rheology for nonlinear viscoelasticity in hectorite suspensions containing poly(ethylene glycol)

The effect of poly(ethylene glycol) (PEG) on the nonlinear viscoelasticity of Laponite suspensions containing NaCl was investigated with large amplitude oscillatory shear rheology. The molecular weight (M_w) of PEG was 4k, 10k and 35k, and the concentration of PEG was varied from 0.063 wt% to 2.4 wt%. The dynamic strain sweep showed that the nonlinearity appeared at γ₀ > 30% with a stress overshoot at γ₀ = 50-70%. The intensity ratio I_3/1 from Fourier-transform increased with γ₀ when entering the nonlinear regime and leveled off at γ₀ ≥ 100% with higher slope and constant value for the PEG of higher M_w or lower concentration. I_3/1 revealed the structure difference in the suspensions induced by adsorbing PEG in the nonlinear regime. The minimum- and large-strain rate viscosities η_M and η_L from the Lissajous curve were found to be sensitive to the nonlinear viscoelasticity and the peak of η_M and η_L appeared at lower γ₀ with higher maximum following the same dependency as I_3/1 on PEG M_w and concentration. The overall nonlinearity parameters N_E and N_V were proposed in this paper and demonstrated to reflect the difference in the Laponite suspensions with PEG more clearly and more effectively.     

Application of FT Rheology to Industrial Linear and Branched Polyethylene Blends

Numerous analytical techniques are used to quantify branching topologies in polyethylene. One of these methods, FT rheology, studies the higher harmonic contributions of the stress response to large amplitude oscillatory shear deformation. The sensitivity of FT rheology in the presence of sparse long‐chain branched chains blended with linear ones is addressed. FT rheology is sensitive even for small concentrations of a partly long‐chain branched component blended with a linear melt (1.5–5 wt.‐%). The non‐linear parameters present a strong dependence on the fraction of long‐chain branched species in a polydisperse melt, the miscibility of which is confirmed via rheological techniques.

     

A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background [1], [2], [3] and [4] and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ₀) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G′(ω) and G″(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In the present review article, we first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations. We then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. We illustrate the utility and sensitivity of these protocols by investigating the nonlinear response of various complex fluids over a wide range of frequency and amplitude of deformation, and show that LAOS characterization is a rigorous test for rheological models and advanced quality control.     

An adaptive parallel tempering method for the dynamic data‐driven parameter estimation of nonlinear models

An adaptive parallel tempering algorithm is developed in a user‐friendly fashion that efficiently and robustly generates near‐optimum solutions. Using adaptive, implicit, time‐integration methods, the method allows fitting model parameters to dynamic data. The proposed approach is relatively insensitive to the initial guess and requires minimal fine‐tuning: most of the algorithm parameters can be determined adaptively based on the analysis of few model simulations, while default values are proposed for the few remaining ones, the exact values of which do not sensitively affect the solution. The method is extensively validated through its application to a number of algebraic and dynamic global optimization problems from Chemical Engineering literature. We then apply it to a multi‐parameter, highly nonlinear, model of the rheology of a thixotropic system where we show how the present approach can be used to robustly determine model parameters by fitting to dynamic, large amplitude, oscillatory stress vs. shear rate, data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1937–1958, 2017     

小振幅振荡剪切法测量PP/(E/VAC)共混物的界面张力

借助于动态流变学中小振幅振荡剪切法测得聚丙烯(PP)与两种不同牌号(乙烯/乙酸乙烯酯)共聚物(E/VAC)共混物的动态模量,通过扫描电子显微镜对共混物中分散相粒径及分布进行表征,将实际测得的共混物动态模量与用Palierne乳液模型计算得到的共混物动态模量进行数据拟合,得到PP与两种不同牌号E/VAC共混物的界面张力分别为0.44 mN/m和1.39 mN/m。