Influence of molecular weight and spinning conditions on the crystalline morphology of polypropylene fibres

In the spinning of polypropylene the “smectic” phase generally appears in the as spun fibres obtained from high fluidity polypropylene (for example M̄_w = 118000) at 200°C and more. The amount of the “smectic” form decreases as the draw down ratio increases. At 200°C and for a draw ratio of 40 the “smectic” form is about 70% of the crystalline phase. At 200°C and for a draw ratio of to 130 or higher, only the monoclinic form is observed. At 180°C, and whatever is the draw ratio, only the monoclinic form is observed. For high-molecular - weight polypropylene (for example M̄_w = 320000) the “smectic” form has never been observed whatever is the spinning temperature within the range 220–260°C. The fibres with high amount of smectic phase show low orientation factors, whereas the fibres having only monoclinic form show the highest orientation factors. These results, compared with elongational behaviour of the polypropylene, suggest that the smectic form appears in the fibres as the elongation rate on the spinning line is lower than the relaxation rate of polypropylene chains.     

Birefringence of polyethylene melt in transient elongational flow at constant strain rate

Simultaneous birefringence and elongational viscosity measurements were carried out on molten commercial grade, low-density polyethylenes during simple elongational flow at constant strain rate and constant temperature. The birefringence increased with time during constant strain rate elongation. The increase in birefringence was a linear function of elongational stress throughout whole elongation, but the elongational viscosity increased in two stages. The increase in elongational viscosity can be divided into linear viscoelastic and nonlnear viscoelastic regions. The linear region appeared at small strain and the nonlinear region appeared at strain greater than 0.7. The elongational viscosity in the nonlinear region increased much more rapidly than that in the linear region. The Gaussian approximation, which is commonly used in molecular models, could be used for the transient elongational flow. A constant stress-optical coefficient C = 1.3 × 10^?10 cm²/dyn was obtained for all the elongational experiments, independent of strain rate (0.002-0.2s^?1). The stress-optical coefficients were weakly dependent on temperature, as predicted by the theory of rubber elasticity.     

Temperature dependence of the conformational relaxation time of polymer molecules in elongational flow: Invariance of the molecular weight exponent

Using an elongational flow technique, we have investigated the relationship between the molecular conformational relaxation time and the molecular weight for a solvent whose quality was altered thermally from near θ to a good solvent state. The materials used were closely monodisperse samples of atactic polystyrene. The results show that the relaxation time τ varies with the molecular weight M as τ ∝ M^1.5, independent of the solvent quality, a result which apparently is at variance with the observed molecular weight dependence of intrinsic viscosity. Despite this invariance of the molecular weight exponent with solvent quality, our results also show that the coils do expand when the solvent quality was increased in agreement with the mean-field theory of Flory.     

Phenomenological analysis of elongational flow birefringence in semidilute solutions of hydroxypropylcellulose

The relaxation time of a polymer chain in an elongational flow field was investigated for hydroxypropylcellulose (HPC) semidilute solution systems by two methods: phenomenological analysis of elongational flow-induced birefringence, and dynamic light scattering (DLS) and rheological measurements. To understand the relaxation time of an entangled semiflexible polymer solution in an elongational flow field, scaling analysis of the elongational flow-induced birefringence curve was performed. The results of both temperature and concentration scaling analyses showed that birefringence curves at different temperatures and at several HPC concentrations were described well by a universal birefringence–strain rate curve. This scaling behavior was compared with the "fuzzy cylinder" model. The critical strain rate corresponded to the correlation time of the slow relaxation mode determined by DLS measurement and the relaxation spectrum obtained by dynamic viscoelasticity measurement. The elongational flow-induced birefringence observed in an HPC semidilute solution was concluded to be attributed to the orientation of the HPC segment in the entangled molecular system, because the dominant relaxation mode is found to be the concentration fluctuation of an entangled molecular cluster in a quiescent state.     

Relaxation characteristics and intrinsic birefringence and viscosity of polystyrene solutions for a wide range of molecular weights

A comparison is made between measurements on polystyrene solutions and the relaxation characteristics and intrinsic birefringence and viscosity given by the theory for the flexible Gaussian chain of variable number of segments and with internal viscosity and internal hydrodynamic interaction. This is done in order to determine the applicability of the theory to polymers over a wide range of molecular weights, including the low molecular weight range in which there may be conflict with the theoretical assumption of chains having a large number of segments. The longest, terminal relaxation time and the number of chain segments are determined from measurements of the frequency dependence of oscillatory flow birefringence while the intrinsic birefringence and viscosity are determined from steady flow measurements. The range of molecular weights studied is from approximately 900 at 10⁶. It is found that the segment weight is approximately 1000 and the number of segments is in direct proportion to the molecular weight for the range from 1 to 1000 segments. The terminal relaxation time has a molecular weight dependence of the type given by the theory but with better agreement for higher molecular weights. While the measured dependences of the intrinsic viscosity and birefringence are in agreement with theory for molecular weights greater than 5 × 10⁴, they deviate significantly for molecular weights below 1 × 10⁴. The ratio of the intrinsic birefringence to intrinsic viscosity, which in theory is a constant independent of molecular weight, is found to change at the lower molecular weights.     

Associating polymers in a well-defined extensional flow field: Influence of solvent quality and polymer concentration

The conformational response of an associating-type random coil macromolecule in solution was investigated utilizing an opposing jet device. This device, capable of generating a well-defined elongational flow field, is quite useful for probing intra- and intermolecular interactions of lightly sulfonated polystyrene ionomers in both nonpolar and polar solvent systems. Below a critical concentration in nonpolar media, such ionomers qualitatively follow trends predicted by dilute solution theory, although intramolecular ionic associations markedly increase the critical elongational shear rate. With further increases in concentration, the extensional behavior is determined by the initial formation of relatively strong intermolecular associations. At even higher polymer concentrations, a third regime is observed where the conformational relaxation process becomes even more facile. On the contrary, in a polar solvent, the conformational relaxation process is markedly enhanced (i.e., critical elongational shear rate is reduced) due to the polyelectrolyte effect, i.e., dissociation of a significant level of the counterions. The effect of this dissociation process influences the relaxation process over the entire concentration region examined. These findings are compared directly with solution rheology, where in low polarity solvents the reduced viscosity is markedly diminished by ion pair-type interactions, and in more polar environments the reduced viscosity is enhanced due to the dissociation of the counterions from the vicinity of the chain backbone.     

聚丙撑碳酸酯的流动性能

聚丙撑碳酸酯的流动性能王胜杰，黄玉惠，丛广民（中国科学院广州化学研究所广州５１０６５０）关键词聚丙撑碳酸酯，流动性能，表观粘度，粘均分子量聚丙撑碳酸酯（ＰＰＣ）是由二氧化碳和环氧丙烷共聚而成的新型含端羟基脂肪族聚碳酸酯［１］，作为对它的基本表征之一，...     

Unraveling the Bimodality of Polypropylene Film Grades Using Rheological Shear and Elongational Measurements: Inconsistent Results of Gel Permeation Chromatography

As the main parameter to describe the molecular structure of a linear polymer, molecular weight distribution of five different polypropylene grades was evaluated through measurements of gel permeation chromatography and rheology experiments. From their dynamic shear data, the relaxation spectra, h(τ), were calculated from which molecular weight distribution was estimated using molecular viscoelastic theories and then compared with the gel permeation chromatography results. Generally good agreement, yet with narrower molecular weight distribution rheology curves was found. Exception was observed for one grade for which rheological data predicted bimodal distribution curve comprising a small shoulder of high molecular weight, not seen in the corresponding gel permeation chromatography curve. Additionally, a higher value of the generalized mixing parameter (i.e. β) was found for this bimodal grade which was attributed to an increase in the number of entanglements per chain and better network connectivity. Furthermore, measurements of the transient extensional viscosity also revealed enhanced strain hardening and melt strength for this particular grade. The results showed that small amount of high molecular weight fraction of linear chains could drastically alter the processing behavior of polypropylene film grades.     

Modification of orientation birefringence of cellulose ester by addition of poly(lactic acid)

Effect of the addition of poly(lactic acid) (PLA) to cellulose acetate propionate (CAP) on the optical anisotropy is studied considering the morphology and molecular orientation. It is found that PLA is miscible with CAP when the amount of PLA is less than 3 wt.%. The dissolution of PLA chains having large intrinsic birefringence into CAP phase enhances the orientation birefringence of a stretched film, although the viscosity and thus the relaxation time of PLA is significantly shorter than those of CAP. The high level of orientation of PLA chains without relaxation is attained by the cooperative alignment with CAP chains. As a result, a retardation film having appropriate birefringence can be designed by polymer blends composed of biomass-based materials. When the amount of PLA is more than 3 wt.%, however, phase separation occurs. In the case of the blends with phase-separated morphology, the orientation birefringence is not greatly enhanced by blending PLA, because the molecular orientation of PLA in PLA phase relaxes immediately as compared with that of CAP.     

The influence of various deformation histories on elongational properties of low density polyethylene

Summary The elongational viscosity of low density polyethylenes depends on the mechanical history as is demonstrated on the samples IUPAC A and IUPAC C and some other specimens. IUPAC C which stems from the same batch as IUPAC A but has undergone an additional extrusion shows a significantly lower elongational viscosity whereas the shear viscosity remains nearly unchanged. The elastic behaviour measured by the recoverable strain is not influenced by a mechanical pretreatment. The viscosity decrease is found to be canceled to its greatest extent after dissolving the sample in xylene and evaporating the solvent. Pure elongation seems to be more effective in creating the viscosity decrease than pure shear. A similar effect could not be found for linear polyethylene and polystyrene. This result leads to the assumption that the branched molecules give rise to a mechanically induced change of the entanglement structure which can be reverted by dissolving. The evidence of the elongational behaviour for film blowing is discussed.Dedicated to Professor Dr. Reif on the occasion of his 60th birthday.     

超高分子量聚苯乙烯的流变性能

以毛细管流变仪和Hakke转矩流变仪对稀土催化合成的超高分子量聚苯乙烯 (UHMWPS)的流变与加工性能进行了研究 .结果表明 ,UHMWPS最显著的流变特征为超高的熔体粘度和低剪切速率下出现不稳定流动 .不稳定流动与超高分子量聚合物长的松弛时间有关 ,并提出了临界剪切速率与分子量和温度的定量关系式 .较低的分子量和较高的温度有利于提高临界剪切速率 ,改善挤出物外观质量和降低熔体粘度 .分子链极度缠结不仅导致超高的熔体粘度 ,也使UHMWPS链解缠加快 ,导致更高的剪切速率敏感性 .UHMWPS塑化时熔体粘度高 ,转矩大 ,加工性能劣于通用聚苯乙烯 (GPPS)     

Brownian dynamics simulation of polyelectrolyte dilute solutions: Relaxation time and elongational flow

The authors used the bead‐and‐spring model and the Brownian dynamics simulation technique including hydrodynamic interaction to study the behavior of dilute polyelectrolyte solutions under elongational flow. First they carried out simulations to determine the longest relaxation time of a polyelectrolyte, finding that the relaxation time depends on the ionic strength of the solution. Then, they studied the coil‐stretch transition of polyelectrolyte molecules in elongational flow and determined the critical value of the elongational rate necessary in order this transition to occur. In this way, they could compute the value of the Deborah number at which coil‐stretch transition sets in for polyelectrolyte dilute solutions. Finally, they studied the power law relationship that relates the critical elongational rate with the molecular weight of the polyelectrolyte. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 714–722, 2007     

Studies on the texture of nematic solutions of a rod-like polymer 1. Distortion of the director field in a magnetic field

The growth of the distortion of the director in an external field, and its relaxation on removal of the field are studied for nematic solutions of the rod-like poly(1,4-phenylene-2,6-benzobisthiazole), PBZT, over a range of concentration, polymer molecular weight and temperature. The twist viscosity and the order parameter are more weakly dependent on concentration than predicted for charged rod-like chains. This behaviour implies a short-range translational order in a direction orthogonal to the chain axis, induced by electrostatic interactions among the polycations on protonated PBZT. The relaxation gives a normal temperature dependence for the splay curvature elasticity, but that for the twist curvature is unexpectedly strong. This behaviour is interpreted as a weakening of the surface anchoring with increased temperature.     

Untypical rheological behaviour of the lignite–carboxymethylcellulose–water dispersion system

Suspensions of lignite in a solution of a high molecular weight carboxymethylcellulose show peculiar rheological behaviour. Unless the lignite concentration is sufficiently high, apparent viscosity and viscoelastic moduli of the suspension are lower than those of the pure solution. This effect is not suppressed by changing pH and seems to be common for low-concentrated suspensions in solutions of high molecular weight (bio)polymer. It is explained by specific structuring of the suspensions. Lignite particles at lower concentration separate long cellulose chains and facilitate their movement under shear flow. The particles loosen inter-chain contacts, disturb and release elastic gel-like structure formed by the long cellulose chains, which results in the low strain oscillatory deformation, the decrease in the moduli and the increase in the loss angle. If the amount of lignite particles is sufficiently high, suspension stiffening occurs as usual. No such effect was observed for suspensions prepared from the low molecular weight derivative. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Effect of composition and structure on rheological properties of styrene-butadiene block copolymers

Styrene-butadiene copolymers of the S-B-S and S-B-S-B-S types, both unmodified and extended with paraffinic-naphthenic oil, were studied by dynamic mechanical spectroscopy and capillary rheometry. In the triblocks at low deformation rates, an increase in 1-vinylethylene unit content leads to an increase in complex dynamic viscosity |η*|. This may be explained by their different supermolecular structure with a higher proportion of long relaxation times. The pentablocks show a considerable effect of molecular parameters on their flow behaviour at low deformation rates. In all the systems, steady viscosity η shows no significant differences at higher shear rates. Obviously the supermolecular structure is disintegrated in these conditions and the effect of chemical structure is negligible. An expected decrease in viscosity in the whole range of deformation rates was observed with the oil-extended copolymer. The dependences of complex dynamic viscosity on angular frequency were compared with those of steady viscosity on shear rate but no unequivocal conclusion as regards the validity of the Cox-Merz rule could be reached.     

黏弹性对介观液珠聚并的影响-液珠-细丝-液珠聚并现象及其分析

在四辊流变仪中,黏弹性高分子介观液滴经反复拉伸和松弛形成了有细丝相连的两个黏弹液珠,研究了黏弹液珠的聚并过程,依形状叫做BSB(bead-string-bead,液珠-细丝-液珠)聚并.BSB现象与常见的通过滴间液膜破裂实现的液滴聚并过程大不相同.根据界面上的Laplace力、液珠移动时的黏性阻力和细丝中黏弹应力之间的平衡,推导出一个力学模型来描述BSB现象,理论分析与实验结果相符较好.细丝直径的变化和稳定性由过程参数和物料参数共同决定,尤其是液滴的黏弹性有较大影响.这一效应对多相高分子与复杂流体加工过程的基础理解富有启发.     

A study of the chain extending effect of elongational flow in polymer solutions

Summary The effect of elongational flow on the orientation of dissolved macromolecules has been studied by observation of localised birefringence within appropriate regions of the flow field, with the objective of linking up experimentally observed chain alignment with basic theory. Benefitting from previous experience the highest available molecular weight fractions were used, i. e. polystyrene ofM _w = 2 · 10⁶, and two opposed suck jets were employed to provide the high strain rates required. Birefringence set in above a critical strain rate and rose rapidly to a maximum value, confirming expectations from theory. Both the maximum birefringence and critical strain rate were independent of concentration indicating that the chains are independent of each other. The value of the birefringence was consistent with complete chain extension, while the critical strain rate yielded a relaxation time of 3 · 10^–5 s in accord with the value calculated fromZimm's non-free draining model. Other observations yielded an estimate of the critical entanglement concentration. The prospects and limitations of the present kind of experimental approach are discussed.With 5 figures and 2 tables     

Elongational flow studies on flexible polymer chains in a pseudo-solvent

The dynamics of isolated high molecular weight (M_H) polymer chains dissolved in a nonentangled semidilute solution of a low molecular weight (M_L) polymer were investigated by monitoring the elongational flow birefringence. Because of its nonentangled nature, a low molecular weight matrix polymer solution is regarded as a pure solvent (a binary pseudo-solvent). A ternary solution consisting of a small amount of a high molecular weight probe polymer and the binary pseudo-solvent is effectively a dilute solution of the probe polymer. It was observed that the birefringence from the orientation and/or stretching of the probe polymer chains starts to increase rather abruptly at a certain critical strain rate, , and the spatial birefringence pattern is localized along the elongation axis, characteristics that are reminiscent of the coil-stretch transition of flexible polymer chains in a simple dilute solution. The relaxation time for the chain extension, _el, defined as the reciprocal of the critical strain rate , was determined at various temperatures, matrix polymer concentrations c_L, and test chain molecular weights M_H. It was found that _el varied with molecular weight as _el~M_H^a , with a ranging from 1.3 to 1.8, which is roughly consistent with the molecular weight dependence of the non-free-draining Zimm relaxation time. A scaled relaxation time _elkT/, which can be used to estimate the radius of gyration R_g of the probe polymer, decreased with increasing c_L, indicating contraction of the high molecular weight polymer due to a screening of the excluded volume effect caused by the matrix polymer in the pseudo-solvent.     

A fluorescence polarization study of the effect of matrix molecular weight on the relaxation of a labeled molecule in a stretched polymer melt

Fluorescence polarization has been used to measure the orientation during stretching of a polystyrene chain embedded in a matrix of narrow-dispersion polystyrene chains of a different molecular weight and labeled by an anthracene group covalently bound at the middle of a chain. Strong coupling between the relaxation of the labeled chain and the matrix chains is evidenced, the orientation of the labeled chain being partially governed by the molecular weight of the matrix. This behavior is interpreted qualitatively on the basis of a molecular model showing that the relaxation of a polymer chain is strongly affected by the entanglements acting on the chain, the number of which is also related to the motion of the surroundings. Good agreement is found between experimental data and the behavior predicted by the model.     

Rheological properties of linear and crosslinked polymer blends: Relation between crosslink density and enhancement of elongational viscosity

Strain‐hardening behavior in the elongational viscosity of binary blends composed of a linear polymer and a crosslinked polymer, in which the molecular chains of the linear polymer were incorporated into the network chains of the crosslinked polymer, was studied. Blending the crosslinked polymer characterized as the gel just beyond the sol–gel transition point greatly enhanced the strain‐hardening behavior in the elongational viscosity, even though the amount of the crosslinked polymer was only 0.3 wt %. However, the crosslinked polymer, which was far beyond or below the sol–gel transition point, had little influence on the elongational viscosity as well as the shear viscosity. The stretching of the chain sections between the crosslink points was responsible for the strain‐hardening behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 228–235, 2001