Effect of comonomers on melt processability of polyacrylonitrile

This work is concerned with the feasibility of achieving melt‐processable polyacrylonitrile copolymer systems as precursors for the manufacture of carbon fibers. Identification of suitable comonomers and achieving the optimum content of the comonomer were some of the main objectives of this investigation. It was seen that methyl acrylate (MA) was found to be suitable for enabling the melt processing of polyacrylonitrile (PAN), in terms of melt viscosity, time stability, and char yield. Below 10 mol % of MA, the PAN copolymer exhibited no flowability, even at very low molecular weights (～ 20,000). The long‐range order inherently present in PAN is speculated to be broken down at a critical value of about 10% MA at 220°C in the PAN‐based system, enabling its melt flowability. It was also seen that the incorporation of MA was seen to improve the temperature and molecular weight window of processability of the PAN system. The molecular weight cutoff for the 90/10 mol % acrylonitrile/methyl acrylate (AN/MA) system was about 50,000 at 220°C, whereas it was increased to about 100,000 in the presence of 15 mol % MA comonomer. Feasibility studies on the use of other comonomers such as higher acrylates and acrylamides were also conducted. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 69–83, 2002     

Effect of rare earth elements' surface treatment on tensile properties and microstructure of glass fiber–reinforced polytetrafluoroethylene composites

Three types of surface modifiers, N‐β‐aminoethyl‐γ‐aminopropyltrimethoxysilane coupling agent (SGS), a mixture of silane and rare earth elements (SGS/RES), and rare earth elements surface modifier (RES), were used to treat the glass fiber surface. Tensile tests of glass fiber–reinforced polytetrafluoroethylene (GF/PTFE) composites with different surface treatment conditions, surface modifiers, and glass fiber content were carried out. Finally, the fracture surface morphologies of GF/PTFE composites were investigated using scanning electron microscopy. Experimental results show that the tensile properties of the treated GF/PTFE composite increased compared with those of the untreated one. RES is superior to SGS/RES and SGS modifiers in promoting interfacial adhesion between the glass fiber and PTFE because of the effects of rare earth elements on the compatibility. Meanwhile, the optimum contents of rare earth elements for the improvement of the tensile properties of GF/PTFE composite were obtained for RES and SGS/RES modifiers. The interfacial adhesion of the GF/PTFE composites treated with RES or SGS/RES modifiers was mainly controlled by the contents of rare earth elements. The tensile properties of the GF/PTFE composites improved considerably when the content of rare earth elements in surface modifiers was 0.2–0.4 wt %, and the optimum tensile performance of GF/PTFE composites was obtained at 0.3 wt % RE content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1667–1672, 2002     

Properties of melt processable PTFE/PEEK blends: The effect of reactive compatibilization using electron beam irradiated melt processable PTFE

For the first time, blends of melt processable polytetrafluoroethylene (MP PTFE) with polyetheretherketone (PEEK) in the MP PTFE/PEEK ratio of 100/0, 80/20, 50/50, 20/80, and 0/100 w/w were prepared and characterized. MP PTFE/PEEK blends are attractive materials due to the combination of low coefficient of friction and universal chemical resistance of MP PTFE with good wear resistance and mechanical strength of PEEK while maintaining high thermal stability of both. Miscibility, phase morphology, and mechanical properties of the new MP PTFE/PEEK blends were investigated. To improve their end‐use properties, an attempt of reactive compounding with the electron beam irradiated MP PTFE (e‐beam MP PTFE) was made. The reactive compounding was done in two steps, that is, the preparation of a masterbatch (MB) consisting of e‐beam MP PTFE/PEEK (50/50 w/w) and subsequent melt blending of MP PTFE/PEEK with varying concentrations of MB. The e‐beam irradiation of MP PTFE carried out in air atmosphere and at room temperature with a dose of 50 kGy results in its chain scission associated with formation of ? COF and ? COOH functional groups. Such modified MP PTFE can be used to compatibilize MP PTFE/PEEK blends. Reactive compatibilized blends exhibit improved phase morphology and mechanical properties. Especially for MP PTFE/PEEK 50/50 blends, a great improvement of almost 250% in strain at break, 40% in stress at break, and more than 600% in toughness was achieved. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reactive polytetrafluoroethylene/polyamide 6 compounds. II. Study of the reactivity with respect to the functionality of the polytetrafluoroethylene component and analysis of the notched impact strength of the polytetrafluoroethylene/polyamide 6 compounds

The formation of block copolymers as a result of an in situ chemical reaction during the reactive extrusion of electron‐beam‐irradiated polytetrafluoroethylene (PTFE) and polyamide 6 (PA) was detected indirectly with differential scanning calorimetry and Fourier transform infrared. As expected, the content of the block copolymers in the compound increased as the irradiation dose was increased. The notched impact strength showed an increase in the PTFE/PA compounds produced with highly irradiated PTFE. This behavior is discussed in the context of the degree of dispersion of the PTFE phase (as reported in part I of this series) and the adhesion changed by the in situ reaction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1317–1324, 2005     

熔体泵在塑料挤出系统中的特性分析

介绍熔体泵的工作原理、结构以及在塑料挤出系统中的应用。     

LDPE熔体在不同角度圆锥口模的挤出流变分析

深入讨论了聚合物熔体在不同角度圆锥口模的挤出胀大现象及机理,利用生产用挤出机进行不同角度的圆锥口模挤出实验,结果表明,圆锥口模挤出过程中,熔体在收敛流道受到拉伸流变,导致强烈的人口弹性效应,表现出显著的挤出胀大。通过实验研究进一步发现,不同的口模人口角对实验材料表现出不同的Bagley校正因子和可回复弹性应变。     

助剂挤出法制备高强度聚四氟乙烯单丝

将聚四氟乙烯(PTFE)与润滑助剂航空煤油混合后均匀挤出,挤出样条脱除助剂,在低于PTFE熔点的温度下高倍拉伸,后经高温紧张热定型,制备高取向PTFE单纤维;通过拉曼光谱、X射线衍射、差示扫描量热分析等方法研究挤出PTFE拉伸过程中材料微细结构的变化,并对PTFE纤维的性能进行表征.结果表明:PTFE在挤出过程中并不会...     

Improving flame retardancy and melt processability of polyethersulfone using low molecular weight additives

The effect of a calcium stearate (CaSt₂) additive on the melt processability and flame retardancy of polyethersulfone (PES) was studied. Measurements of the viscosity of PES and its composites showed a marked decrease in viscosity with increase in the fraction of CaSt₂ additive. About 40% reduction in viscosity of PES was achieved with addition of 5 wt % CaSt₂. By decreasing the viscosity, the CaSt₂ additive enabled the melt extrusion of PES at lower temperatures up to 90 °C below that of conventional melt processing. The flammability was also investigated using a Pyrolysis Combustion Flow Calorimeter (PCFC). The CaSt₂ additive resulted in tremendous improvement in the flame retardancy of PES as evident in the reduction of the heat release capacity (HRC) of the composites by up to 37%. Moreover, the peak of heat release rate (pHRR) of PES in the composites was up to 84% lower than in the neat polymer. The remarkable improvement in flame retardancy of PES was demonstrated to be related to the rapid charring of the composites and the in situ formation of calcium carbonate/calcium oxide upon decomposition of CaSt₂. The CaSt₂ additive was also found to enhance the flame retardancy of thermoplastics including polyamide‐6 and polypropylene (PP). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43525.     

通过反应挤出提高聚丙烯的熔体强度

利用反应挤出技术研究了不同反应物对聚丙烯(PP)熔体强度的影响。考察了不同用量的低密度聚乙烯(LDPE)、乙烯-乙酸乙烯酯共聚物(EVA)、季戊四醇三丙烯酸酯(PETA)、二乙烯基苯(DVB)以及上述物质的混合物在过氧化二异丙苯的引发下对PP熔体强度、熔体流动速率、熔垂的影响。结果表明,LDPE、EVA的加入对产物熔体强度的影响有限,PFTA也只能使其提高1倍左右;而DVB的加入可使产物的熔体强度显著提高,仅加入1％就可使熔体强度提高20倍,熔垂实验也证明了这一点;几种反应物混合使用效果不如单独使用好。     

Reactive polytetrafluoroethylene/polyamide compounds. I. Characterization of the compound morphology with respect to the functionality of the polytetrafluoroethylene component by microscopic and differential scanning calorimetry studies

Compounds of electron‐beam‐irradiated polytetrafluoroethylene (PTFE) and polyamide (PA) were produced by reactive extrusion. During extrusion, both a breakdown process of the PTFE agglomerates and a chemical reaction between PTFE and PA took place. The morphology of the compounds was characterized with differential scanning calorimetry using fractionated crystallization, with atomic force microscopy and scanning electron microscopy, and with dynamic light scattering. The particle size of the dispersed PTFE phase decreased as the irradiation dose increased. A simple theoretical model of the breakdown process of PTFE agglomerates was made for the discussion of the development of the observed degree of dispersion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1308–1316, 2005     

聚乙烯熔融挤出接枝α—甲基丙烯酸

通过聚乙烯熔啧挤出接枝甲基丙烯酸（MAA）,研究了各种因素对LDPE接枝率及熔体流动速率的影响,研究表明,MAA用量对接枝率影响较大,而引发剂用量对接枝率影响不大;丙烯酸（AA）的加入提高了接枝率和熔体流动速率,而另入马来酸酐（MAH）接枝率则反而下降;DCP／BOP为4／1时接枝率最高,阻交联剂的加入提高了熔体流动速率,但降低了接枝率。     

Direct Melt Extrusion Processing of Nylon 6/Clay Nanocomposites Based on Pristine Montmorillonite

Summary: An original direct melt extrusion processing of nylon 6/clay nanocomposites was reported based on pristine (Na⁺‐based) montmorillonite as well as a simple approach using a typical two‐screw extruder. By the application of intercalation agents as the thermodynamic assistants, this method is as an appropriate procedure for industrialized manufacture together with much lowered production cost. Interestingly enough, the synergistic effects of montmorillonite with other inorganic particulates was observed for the first time here.

X‐ray diffraction patterns of pristine MMT and nylon 6/MMT composites with grouped intercalation agents.     

Effect of vibration on rheology of polymer melt

In this article, under shearing vibration and pressure vibration, the rheological behavior of HDPE, ABS, and PS melts and the mechanical properties of molded parts are studied. The experimental results show that, under the vibration condition, the apparent viscosity of the polymer melt decreases with an increasing of the vibration frequency and amplitude applied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1587–1592, 2002     

Hot Melt Reactive Extrusion of Chitosan with Poly(acrylic acid)

The hot melt reactive extrusion of blends of chitosan and poly(acrylic acid) (PAA) was carried out without any process additives such as organic solvent or plasticizer. The maximum amount of chitosan in the blend during the extrusion process was kept at 40 wt%, since the melt viscosity of a system containing 50 wt% of chitosan exceeded the torque limitation of the equipment. The carboxylic groups of PAA interacted with the amine groups of chitosan during the melt process, and the system exhibited good melt flow. The interactions between these two polymers were explained by investigating the results obtained by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal transition behavior of PAA was altered with a decrease of more than 10°C in the peak melting point after extrusion. The infrared (IR) spectroscopic data confirmed the existence of a complex formation and possible hydrogen bonding between chitosan and PAA during the melt process. Scanning electron microscopy (SEM) micrographs indicated that chitosan was well-dispersed in the PAA blends up to 30 wt% chitosan, with no indication of loose particles or other disruptions on the upper and lower fractured faces. This smooth interface might have been caused by the interaction between amide bonds of chitosan and carboxylic groups of PAA.     

Study of poly(ethylene terephthalate)/polypropylene microfibrillar composites. I. Morphological development in melt extrusion

Poly(ethylene terephthalate)/polypropylene (PET/PP) blends of different compositions were extruded through a 2‐mm capillary die using a corotating twin‐screw extruder. The extrudates were cryogenically fractured and examined using scanning electron microscopy. The viscosity ratio of the constituent polymers alone was found to be unsuitable for explaining the polymer blend morphology. At a PET concentration of 20%, the extrudate consists of three regions. The skin layer, which is about 10 μm thick, has a lower concentration of the dispersed PET phase than the overall concentration. The intermediate region, which is about 400 μm thick, has profuse PET fibers and some small PET particles. The central region, which is approximately 800 μm in diameter, mainly contains PET particles that are generally bigger. A low barrel temperature, low die temperature, and fast cooling rate helped to retain the fibers near the extrudate skin. Meanwhile, the variation of the barrel temperature, die temperature, and cooling media did not produce a significant affect on the PET particle size distribution in the central region of the extrudate. A high screw speed and a high postextrusion drawing speed were very effective in producing fibers in the extrudates through elongation of particles. At a PET concentration of 30%, coalescence of the PET phase was prevalent, leading to the formation of PET platelets near the extrudate skin and irregular PET networks in the central region of the extrudate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1743–1752, 2003     

热处理时间对熔纺聚氨酯纤维性能的影响

讨论预聚体法生产的熔纺酯型聚氨酯纤维在 80℃下热处理时间对其性能的影响。结果表明 :该纤维的热处理一段时间后线密度随热处理时间的增加而增加 ,强度开始随热处理时间增加而提高 ,但随着时间进一步增加而下降 ;断裂伸长率 ,沸水收缩率随热处理时间的增加而降低 ,热处理时间对纤维的干热和湿热收缩率影响不大     

Melt electrospinning of low‐density polyethylene having a low‐melt flow index

Melt electrospinning is a cheaper, more environmentally friendly, and safer alternative to solution electrospinning. We have designed a novel melt spinning device which incorporates a reverse of the normal polarity, with the capillary grounded and the collector grid at positive potential. The apparatus is much simpler and more economical than conventional equipment because no syringe pump is required. Low‐density polyethylene (LDPE) with a low‐melt flow index of 2 g/10 min, which is not suitable for spinning using current commercial methods, was chosen to highlight the advantages of melt electrospinning in general, and our device in particular. The effects of varying the electrospinning parameters such as temperature, electrostatic field, spinning distance, and capillary inner diameter, have been studied. Although it was found that temperatures higher than normal processing temperatures had to be employed in our electrospinning system to reduce the viscosity of the polymer melt sufficiently, good quality fibers with smooth and even surfaces, most of which had diameters smaller than 15 μm, were electrospun successfully. It was observed that there was an optimum point for the spinning distance (14–15 cm) and the capillary inner diameter (0.4–0.6 mm) to get fine fiber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

聚丙烯熔融挤出接枝马来酸酐的研究

研究了通过双螺杆挤出机聚丙烯熔融挤出接枝马来酸酐制马来酸酐接枝聚丙烯（PP—g—MAH）的工艺，包括单体马来酸酐（MAH）、引发剂DCP的用量及熔融反应温度和时间对聚丙烯（PP）熔融接枝MAH的接枝率的影响。结果表明：DCP、MAH的用量对PP—g—MAH接枝率影响比较明显，其最佳配比为DCP0．15份、MAH2份；最佳工艺条件为挤出螺杆转速40r／min，反应温度195-200℃。     

聚四氟乙烯原位纤维化对TPEE/PTFE复合材料发泡行为的影响

通过熔融共混法研究了不同加工工艺对聚四氟乙烯（PTFE）纤维化的影响,制备了热塑性聚酯弹性体（TPEE）/PTFE纳米纤维复合材料。在此基础上,研究了PTFE含量对TPEE的结晶行为、流变行为以及发泡行为的影响。结果表明,PTFE纤维可以促进TPEE结晶,改善TPEE的流变性能。纳米纤维的高比表面积为泡孔成核提供了大量成核位点,有效提高了泡孔密度,降低了泡孔尺寸;当PTFE含量为2份时,制备了平均泡孔直径为3.2 μm,平均泡孔密度为3.11×10¹⁰ 个/cm³的复合材料泡沫。