Regeneration of Bombyx mori silk by electrospinning—part 1: processing parameters and geometric properties

We studied the effect of electrospinning parameters on the morphology and fiber diameter of regenerated silk from Bombyx mori. Effects of electric field and tip-to-collection plate distances of various silk concentrations in formic acid on fiber uniformity, morphology and diameter were measured. Statistical analysis showed that the silk concentration was the most important parameter in producing uniform cylindrical fibers less than 100 nm in diameter.     

The characterization of rheological properties of melt grafting polypropylene for foaming

Large enhancements of the melt strength of polypropylene (PP) were achieved by the introduction of specific unsaturated linear polyester (ULP) branches using melt grafting. The transient torque curves and optical rheology microscope images indicated that branching reactions took place and the ULP had been grafted onto the PP backbone. Shear rheological behaviors of three kinds of PP were investigated using rotational rheometer under dynamic shear mode with periodic shear rate. These PP samples are foamable PP (FPP) with sparse branches obtained by grafting ULP, commercial high melt strength PP (HMS PP) for foaming and conventional linear PP (EPS). It was found that the rheological properties of FPP, the HMS PP, were distinctly different from those of conventional PP. Storage modulus, steady state compliance and zero shear viscosity increased in comparison with EPS, while shear viscosity decreased. This result implied the presence of branching structures that was not revealed in conventional PP. In melt flow measurements, extrusion swell that was a prominent behavior of branching PP was observed also for FPP and PF. Compared to linear PP, FPP and PF showed distinct sag-resistant property and lower melt flow index. On the other hand, to estimate the extent of branching, a detailed method was applied using the obtained zero shear viscosity. The result showed that FPP was grafted by sparse ULP. From these results, it was found that FPP showed obvious enhancements in rheological behaviors similar to PF, although its melt strength was lower than that of PF due to the presence of shorter branching chains grafted on the backbone of FPP.     

Electrospinning of polymer melts: Phenomenological observations

Melt electrospinning is an alternative to solution electrospinning, however, melt electrospinning has typically resulted in fibers with diameters of tens of microns. In this paper we demonstrate that polypropylene fibers can be reduced from 35 ± 8 μm in diameter, to 840 ± 190 nm with a viscosity-reducing additive. Melt electrospun blends of poly(ethylene glycol)-block-poly(?-caprolactone) (PEG₄₇-b-PCL₉₅) and poly(?-caprolactone) (PCL) produced fibers with micron-scale diameters (2.0 ± 0.3 μm); this was lowered to 270 ± 100 nm by using the gap method of alignment for collection. The collected melt electrospun fibers often fused together where they touched, allowing the stabilization of relatively thick non-woven felts. The melt electrospun collection also included coiled circles and looped patterns of fibers approximately 150-250 μm in diameter. The polymer jet was visible between the collector and spinneret for particularly significant lengths, and underwent coiling and buckling instabilities close to the collector. The focused deposition of melt electrospun fibers was maintained when multiple jets were observed, with the collections from multiple jets separated by 3.8 ± 0.5 mm for a 5 cm collector gap. The frequent fusion points between melt electrospun fibers, and a reduction in diameter for the gap method of alignment, indicated that the melt electrospun fibers are still slightly molten at collection.     

Impact of processing history on rheological properties for branched polypropylene

The impact of applied processing history and the post-processing annealing procedure on the rheological properties of long-chain branched polypropylene (B-PP) have been studied intensively as compared with conventional linear polypropylene (L-PP) and low-density polyethylene (LDPE) produced by autoclave process. It was found that drawdown force, as a measure of melt elasticity for B-PP, is greatly depressed even by the short-time processing in an internal batch mixer, whereas the rheological properties of L-PP are unchanged by the processing history. Considering that the drawdown force is recovered to the original value during the post-processing annealing, the phenomenon is ascribed to the conformation change related to the branch structure, i.e. the alignment of long branches to a backbone chain, which is known as ‘shear modification’. Further, it is demonstrated that the depression of the drawdown force for B-PP is more significant than that for LDPE. Moreover, it is also clarified that B-PP needs a longer post-processing annealing time to recover the drawdown force than LDPE. The difference in the recovery curves during the annealing suggests that B-PP has less relatively ‘short’ long branches.     

Melt Rheological and Impact Properties of Thermally Stable PP/mLLDPE Blends

Effect of the heat stabilizer on the melt rheological properties of the blends of polypropylene (PP) with mLLDPE (mettalocene linear low density polyethylene), after thermal degradation in an air oven, was studied. Study carried out is presented to describe the effect of blending ratio and presence of stabilizer on shear stress, shear rate, melt viscosity and melt elasticity parameters. In general, blending of PP with mLLDPE results in an increased viscosity. The viscosity of PP abruptly decreases after the thermal degradation. Interestingly the melt viscosity PP/mLLDPE blend does not show such a marked decrease. This shows that mLLDPE not only acts as an impact modifier but also acts as a thermal stabilizer. The presence of stabilizer in both materials has not shown much difference in melt viscosity thereby suggesting adequate stabilization of the blend system.     

Water-assisted extrusion as a novel processing route to prepare polypropylene/halloysite nanotube nanocomposites: Structure and properties

Naturally occurring halloysite nanotubes (HNTs) are used to prepare Polypropylene (PP)/HNTs nanocomposites using a novel “one step” water-assisted extrusion process with and without the use of a PP-graft-maleic anhydride (PP-g-MA) as compatibilizer. In order to analyze the influence of PP-g-MA and/or water injection on the HNTs dispersion and therefore on nanocomposite properties, structural analysis (SEM and TEM) is combined with rheological and thermo-mechanical experiments. The best clay dispersion is obtained when compatibilizer and water injection are combined together (synergistic effect). As a consequence, the linear viscoelastic properties and the dynamic storage modulus are dramatically enhanced for this system. A mechanism explaining the interaction between HNTs and PP-g-MA in presence of water is proposed. The thermal stability and flame retardant property are also investigated. Thermal analyses reveal two opposite effects of HNTs on the thermal behaviour of PP. A surface catalytic action of the halloysite speeds up thermal degradation of PP. However, this effect is reduced with improved HNTs dispersion, presumably via an entrapment mechanism of the decomposition products inside the lumens. Finally, cone calorimeter results show that low flammability of nanocomposites is only achieved when combining water injection and PP-g-MA. In view of these results, PP/HNTs nanocomposites prepared using this novel processing route are promising candidates for flame retardant applications.     

聚丙烯/凹凸棒土复合材料的制备与性能研究

以聚丙烯(PP)为基体,凹凸棒土(AT)为无机粒子填充剂,通过熔融共混的方法制备PP/AT复合材料,探讨了AT对PP/AT复合材料的热行为、机械性能及流动性能的影响.结果表明:AT能起到一定增强的效果,当AT的含量为2 wt.%时,PP/AT复合材料的抗拉强度可达到35.5MPa,但其冲击强度随AT含量的增加而呈现阶梯...     

Ultrasonic Degradation Studies and Its Effect on Thermal Properties of Polypropylene

In this article, the ultrasonic degradation of polypropylene (PP) melt was conducted in a specially designed reactor. Dynamic stress rheometer and gel permeation chromatography (GPC) were used to study the degradation behavior of PP melt. Thermal properties of ultrasonically treated PP were further discussed. The results showed the decrease of complex viscosity, zero shear viscosity, representative relaxation time, viscoelastic moduli as well as cross-over modulus, but an increase of cross-over frequency with introduction of ultrasonic irradiation, due to reduction of weight average molecular weight and increase of molecular weight distribution index of the polymer. The ultrasonic chain scissions of PP melt mainly occurred at the initial 3 min of irradiation and subsequently tended to terminate under our experimental conditions. In addition, the crystallization temperature and melting temperature of PP together got decreased in the presence of ultrasonic irradiation due to the occurrence of lower molecular weight components and some chemical irregularities in PP chain, along with the slight increase of crystallinity.     

Crystallization and morphology of the trigonal form in random propene/1-pentene copolymers

The melting and crystallization behaviour of a series of isotactic propene/1-pentene random copolymers, with 1-pentene contents up to 50 mol%, was investigated by DSC and temperature resolved WAXD/SAXS. The role of the 1-pentene comonomer in the development of the trigonal modification (δ-form) of i-PP was studied and the results were compared with those reported in the literature for PP copolymers with 1-hexene. The crystallizing capability of the δ-form, which develops in the composition range between ca. 10 and 50 mol% of 1-pentene content, only slightly decreases with concentration of 1-pentene. This result is correlated with the limits imposed to cell expansion by the crystal density. The crystallinity degree calculated from the deconvolution of the WAXD patterns is in fair agreement with the results of the DSC analysis, from which the value of the melting enthalpy of the perfect i-PP δ-form has been estimated to be around 140 J/g. The crystallization kinetics of the trigonal modification is characterized by a composition-dependent induction time followed by a relatively fast development of structural order. The sharp WAXD reflections combined with the SAXS data suggest that, notwithstanding the intrinsic intrachain structural disorder, thin and wide lamellae characterize the morphology of the δ-form crystallites.     

The melt grafting preparation and rheological characterization of long chain branching polypropylene

To study the rheological properties of long chain branching (LCB) polypropylene (PP), long chain branches (LCB) were grafted onto the linear PP by melt grafting reaction in the presence of a novel chain extender, poly(hexamethylendiamine-guanidine hydrochloride) (PHGH). The branching reactions between the functionalized PP and PHGH were confirmed by transient torque curves and FTIR. By differential scanning calorimetry (DSC) and polarized microscope measurements, the presence of long chain branching structures was further confirmed. Also, the viscoelastic properties of the LCB PP and linear PP under shear flow were investigated for distinguishing LCB PP from linear PP. It was found that the elastic response of LCB PP at low frequencies was significantly enhanced in comparison with that of the linear PP, implying a presence of a long relaxation time mode that was not revealed in linear PP. Moreover, the branching levels of LCB PP were quantified using a detailed method, which was in correspondence with the molar amount of PHGH grafted on PP.     

高极性聚丙烯的制备及其应用研究

利用双组分熔融接枝极性单体的方法,制备高极性聚丙烯材料。红外光谱和熔融指数表明,采用多组分熔融接枝体系,通过加入苯乙烯单体,能够有效地控制单组分熔融接枝聚丙烯体系中严重的聚丙烯降解反应,大幅度提高极性单体的接枝率,同时保持了聚丙烯优良的力学性能,从而获得一种力学性能优良的高极性聚丙烯材料。     

聚丙烯／蒙脱土纳米复合材料的制备与性能

用烷基季铵盐对钠基蒙脱土进行有机化处理,使其成为有机蒙脱土。X射线衍射（XRD）表明有机阳离子已同钠离子发生离子交换作用,导致层间距扩大。用熔融插层法制备聚丙烯／蒙脱土纳米复合材料,测试了力学性能。通过XRD、DSC等手段研究了其结构与结晶行为,并与聚丙烯进行了对比。实验表明,通过熔融插层可使聚丙烯插层于蒙脱土片层之中,且所得聚合物的冲击强度有所提高。     

Glass bead-filled polypropylene part I: Rheological and mechanical properties

Five glass bead-filled polypropylene composites were rheologically characterized at 240°C using two rotational rheometers to obtain low shear-rate data and a capillary rheometer to obtain high shear-rate data. Both steady and dynamic properties were measured at low shear rates. Each composite was also injection molded into tensile and flexural test bars for a mechanical properties profile at 25°C. The tensile modulus was determined from a simple extensional deformation whereas the flexural modulus was determined from a three-point-bend test. The relative shear viscosity and relative loss modulus are different nonlinear functions of the volume fraction of beads at a constant shear rate, while the relative storage modulus appears to be a linear function of bead fraction. The relative viscosity decreases with increasing shear rate and the zero shear-rate data are in very good agreement with the Guth-Gold equation. The relative tensile modulus and relative flexural modulus are each linear functions of bead fraction over the entire range of filler concentration, 0-29 vol percent. From these data it is concluded that a simple correspondence between slow viscous flow and small strain elasticity does not exist for these composites.     

Effect of processing conditions and properties of PP/nylon 6 blends

Polypropylene (PP) and nylon 6 were melt blended in a twin screw extruder at different screw speeds using malefic anhydride grafted polypropylene (MA-g-PP) as a compatibilizer. Different compositions were injection moulded and the mechanical properties, rheological behaviour and morphology of the resulting blends were studied. The impact strength and tensile strength of PP increased due to the addition of nylon 6 and MA-g-PP acted as a compatibilizer. Mechanical data suggested that blending at higher shear rates-gave better properties. An amount of compatibilizer at the 3 parts level offered optimum properties.     

聚丙烯及聚苯乙烯发泡体系熔体密度的研究

通过高压毛细管流变仪测量聚丙烯发泡体系的PVT关系,得到一定压力和温度下聚丙烯发泡体系的熔体密度,用于分析发泡体系的毛细管流变特性。与聚苯乙烯和高冲击强度聚苯乙烯发泡体系的熔体密度进行了对比,研究并分析了温度、压力、发泡剂及成核剂含量对发泡体系熔体密度的影响。结果表明:发泡体系的熔体密度均随压力的增大而提高,随温度的升高而降低;在发泡气体的临界压力处,发泡体系的熔体密度产生突变;高压下,发泡剂与成核剂含量对熔体密度的影响很小。     

硅藻土含量及粒径对聚丙烯复合材料流动特性的影响

应用熔体流动速率仪测量了3种硅藻土填充聚丙烯复合材料的熔体体积流动速率(MVR),以考察填料含量和粒径对复合体系流动特性的影响。结果表明:复合材料的MVR随着温度的提高和载荷的增加而呈非线性函数形式增大;而随着填料体积分数和粒径的增加而下降。     

PP/有机改性蒙脱土纳米复合材料的性能

采用熔融插层法制备了聚丙烯/有机改性蒙脱土(PP/OMMT)纳米复合材料,研究了OMMT用量对PP基体力学性能和阻燃性能的影响,利用透射电镜(TEM)分析了OMMT在PP基体中的分散性。结果表明:OMMT的加入有助于提高PP基体的力学性能和阻燃性能;熔融插层法可以使PP的大分子链有效地插入OMMT的片层之间;随着OMMT用量的增加,其在PP基体中的分散性变差。     

Influence of the processing parameters on needleless electrospinning from double ring slits spinneret using response surface methodology

Needleless electrospinning technology was an effective processing method which can fabricate large scale nanofibers. We first developed a novel double rings slit spinneret to overcome the shortcomings of current needleless electrospinning spinnerets. The solution of the flow rate was controlled accurately by peristaltic control pump. Response surface methodology was adopted to investigate the influence of the processing parameters on the morphology and diameter of nanofibers. The main spinning processing parameters comprised solution concentration, applied voltage, collection distance and solution flow rate. The analysis of variance was used to evaluate response surface reduced quadratic model for nanofiber diameter. The linear and quadratic coefficients were obtained. The morphology of nanofibers was observed by scanning electron microscopy. Effects of different processing parameters on the nanofiber mean diameter have been discussed. Predicated values have a good agreement with actual values for nanofiber diameter. Actual nanofiber diameter ranges from129.15 to 404.70 nm with different process parameters. Mechanical properties of nanofiber membrane have been investigated. High quality and high throughout nanofiber could be continuously produced. This novel needleless electrospinning spinneret has a great potential for large scale nanofibers production to promote electrospinning technology development. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46407.     

Properties of elongational flow injection-molded polyethylene part 2: Influence of processing parameters

In the first part of this series, the influence of mold geometry was examined with reference to the improvement of the mechanical properties of elongational flow injection-molded polyethylene. In the present study (Part 2), processing parameters have been investigated and the physical properties of the moldings examined. It is confirmed that mainly two parameters, the temperature of the melt and the pressure on the solidifying mold, govern the injection process. Results are discussed in terms of the molecular orientation that is developed during the filling process and depends on the temperature of the melt. The application of high pressures leads to a pressure-induced crystallization effect that freezes in the molecular orientation within the mold.     

Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters

In the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008