拉伸温度对UHMW-PE/HDPE共混纤维结晶性能的影响

通过熔融纺丝工艺成功制备了超高分子量聚乙烯(UHMW-PE)/高密度聚乙烯(HDPE)共混初生丝,并将初生丝在不同温度下进行高倍率热拉伸制得UHMW-PE/HDPE共混纤维。采用广角X射线衍射(WAXD)、差示扫描量热(DSC)、拉伸试验等方法探讨了不同热拉伸温度下获得的UHMW-PE/HDPE共混纤维的微观结构及力学性能。结果表明,在85℃下拉伸所得的纤维具有最高的结晶度、结晶取向度以及最细长的晶粒形状,纤维的力学性能也最优。太低的拉伸温度不利于纤维的分子链以及晶体结构沿轴向取向,太高的拉伸温度则不利于纤维的晶体结构在拉伸过程中进行重组,因此太低或太高的拉伸温度均不利于纤维力学性能的提升。     

PMMA/PET共混体系可纺性及纤维的结构与性能

研究了PMMA/PET共混纤维的可纺性和拉伸性,并测定了拉伸丝的力学性能、取向和结晶结构。结果表明,PMMA的加入可以延迟PET的成形,减小纤维的取向,提高PMMA/PET卷绕丝的断裂伸长,从而提高纤维的后拉伸倍数,提高纤维的生产效率;PMMA的加入量在5％以下时,不影响纤维的可纺性;PMMA/PET共混纤维拉伸丝的强度和断裂伸长可达到常规PET纤维的要求;扫描电镜照片显示,PMMA以棒状形式分散在PET基体中,分散直径为1μm左右。     

油嘴结构对涤纶FDY染色条纹丝的影响

在热辊拉伸式涤纶全拉伸丝(FDY)生产中,采用油嘴上油,会产生涤纶FDY染色条纹丝。使用不同型号的油嘴用于生产涤纶FDY,分析了油嘴结构对染色条纹丝的影响。结果表明:在正常生产工艺条件下,初生丝从油嘴中吸附的油剂量不均匀导致纤维局部取向度和结晶度低是产生染色条纹丝的主要原因;油嘴的结构决定了初生丝的上油均匀性,贮油槽贮油能力越大,吸油和放油能力越强,上油均匀性越好,油嘴丝道宽度对上油均匀性也有一定的影响;生产中选择合适的油嘴,可提高初生丝的上油均匀性,从而减少涤纶FDY染色条纹丝的产生。     

拉伸与热定型对聚苯硫醚长丝结构性能的影响

以国产聚苯硫醚(PPS)树脂为原料,用熔融法纺丝制得PPS长丝。采用差示扫描量热仪、热重分析仪研究了后处理对纤维结晶和热性能的影响;利用声速取向测量仪研究了拉伸对纤维取向的影响;用单纱电子强力仪测量了纤维力学性能。结果表明:热拉伸倍数增大,PPS纤维取向度、结晶度增加,纤维的断裂强度增加,断裂伸长减小;拉伸倍数大于5,会出现较多毛丝和断头;控制热拉伸温度85～105℃,热定型温度100℃以上;纤维的结晶主要在热拉伸过程中基本完成,热定型进一步完善结晶结构;高温下氧气的存在,会使PPS纤维发生严重的氧化降解。     

PMMA／PBT共混体系可纺性及纤维的结构与性能

研究了PMMA／PBT共混纤维的可纺性和拉伸性，并测定了拉伸丝的力学性能、取向和结晶结构。结果表明，PMMA的加入可以延迟PET的成形，减小纤维的取向，提高PMMA／PBT卷绕丝的断裂伸长，从而提高纤维的后拉伸倍数，提高纤维的生产效率；PMMA的加入量在5％以下时，不影响纤维的可纺性；PMMA／PBT共混纤维拉伸丝的强度和断裂伸长可达到常规PET纤维的要求；扫描电镜照片显示，PMMA以棒状形式分散在PET基体中，分散直径为1μm左右。     

聚甲醛纤维的制备及其力学性能研究

采用双螺杆熔融纺丝制得聚甲醛(POM)卷绕丝,通过水浴拉伸卷绕制得聚甲醛纤维。利用声速取向测试仪研究了拉伸对纤维取向的影响;利用纤维强度仪测量了纤维的力学性能,研究了拉伸温度、热定形条件、酸碱性环境对纤维力学性能的影响。结果表明:拉伸倍数增大,POM纤维的取向度、断裂强度、模量增大,断裂伸长率减小;控制水浴拉伸温度在80~95℃为宜;紧张热定形有利于提高纤维力学性能。制得的聚甲醛纤维耐碱性优良,有一定的耐酸性能。     

PTT的纺丝稳定性和聚集态结构

利用毛细管流变仪研究PTT熔体挤出时的破裂现象,讨论PTT纺丝稳定性和初生纤维聚集态结构。结屎表明,PTT熔体是一种拉伸变稀型流体。自由挤出时,即使剪切速率达到1.5×105 s-1时,挤出熔体也没有出现明显的熔体破裂;而在纺丝过程中,在卷绕速度达到3.8 km／min(剪切速率2.1×103 s-1)时,就出现明显的熔体断裂现象。在高速纺丝中,控制PTT初生纤维取向结构的关键是喷丝头拉伸比,决定结晶结构的关键是卷绕速度。增加喷丝头拉伸比可以提高初生纤维的取向度;提高卷绕速度可以提高纤维结晶度。     

熔纺PE⁃UHMW/PE⁃HD共混纤维的力学性能和晶体结构研究

通过熔融纺丝工艺制备了拉伸强度为1.13 GPa的超高分子量聚乙烯（PE?UHMW）/高密度聚乙烯（PE?HD）共混纤维。采用差示扫描量热仪（DSC）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）、声速取向测试、纤维强度测试等方法研究了初生丝和纤维的晶体结构及力学性能。结果表明,将PE?UHMW与低熔体流动速率（MFR）的PE?HD共混后,提高了共混纤维的分子链取向度、结晶度及力学性能;由高度取向的分子链形成的晶粒可以在轴向上被有效拉伸,形成更规则和致密的晶体结构,从而提高了纤维的力学性能。     

聚酯纤维的热管纺丝

<正> 本文介绍了ICI纤维研究部成员对聚酯纤维热管纺丝所做的研究工作,其中Frank.Smith集中探讨了机理,Malcolm Staveley着重研究了工艺。 当卷绕速度增加时,聚酯初生丝的力学性能相应得到提高。但是,即使采用4000m/min的工艺过程,所得到的预取向丝POY仍然须要补充后拉伸,以获得所需要的力学性能。然而,人们发现,如果将一根由200℃     

聚酯纤维微观形态结构与老化特性的关系

通过力学性能测试研究了高强型聚酯工业丝(HT-PET)和聚酯全拉伸丝(FDY-PET)在人工加速老化条件下的性能变化,并通过特性黏度、红外光谱、广角X射线散射、小角X射线散射对纤维在老化过程中的分子和微观形态结构变化进行了表征。结果表明:在试验设定的人工加速老化条件下,FDYPET纤维的断裂强度和断裂伸长率都明显下降,沸水收缩率降低,而HT-PET纤维的力学性能没有显著变化。形态结构分析表明:两种纤维的端羧基含量相近,但在老化过程中,FDY-PET纤维的端羧基明显增多,特性黏度减小,晶区含量、微纤和片晶尺寸以及取向程度都发生显著变化,这是纤维力学性能变化的主要因素;而HT-PET纤维结构稳定,超分子结构和微观形态结构变化不明显,老化过程中只发生了少量无定形区的收缩,引起取向度有所下降,对纤维的力学性能影响不大。     

The preparation of high performance silk fiber/fibroin composite

An all-silk composite, in which uniaxially-aligned and continuous-typed Bombyx mori silk fibers were embedded in a matrix of silk protein (fibroin), was successfully prepared via a solution casting process. The structure, morphology, mechanical and thermal properties of such silk fiber/fibroin composites were investigated with X-ray diffraction, scanning electron microscopy, tensile and compression tests, dynamic mechanical analysis and thermogravimetric analysis. The results demonstrated that the interface adhesion between silk fiber and the fibroin matrix was enhanced by controlling the fiber dissolution through 6 mol L⁻¹ LiBr aqueous solution. Compare to those of the pure fibroin counterparts, the overall mechanical properties as well as the thermal stability of such silk fiber/fibroin composites were significantly improved. For example, the composite with 25 wt% fibers showed a breaking stress of 151 MPa and a breaking elongation of 27.1% in the direction parallel to the fiber array, and a compression modulus of 1.1 GPa in the perpendicular direction. The pure fibroin matrix (film), on the other hand, typically had a breaking stress of 60 MPa, a breaking elongation of 2.1% and a compression modulus of 0.5 GPa, respectively. This work suggests that such a controllable technique may help in the preparation of animal silk based materials with promising properties for various applications.     

Dissolution and characterization of regenerated Antheraea pernyi silk fibroin

Dissolution of Antheraea pernyi silk fiber was carried out in a calcium nitrate solution with various dissolving conditions. The solubility was significantly dependent on the concentration of calcium nitrate, dissolving temperature, and time. The proper conditions of dissolution were found as 7M calcium nitrate, 100°C temperature, and 3 h dissolving time. The aqueous solution of A. pernyi silk fibroin was composed of a mixture of polypeptides with several molecular weights above 14 kDa. FTIR and XRD showed that regenerated A. pernyi silk fibroin was composed of an α-helix as well as a random-coil conformation while silk fiber had a traditional β-sheet structure. The endo–exo transition in the temperature ranges of 228–232°C also supports these conformations of regenerated silk fibroin film. TGA and DTG curves showed that the thermal decomposition of regenerated A. pernyi silk fibroin proceeded by three steps, not dependent on the conformation. The mechanical damping peaks (tan δ) appeared about 227°C with a minor shoulder maximum about 240°C, which were somewhat lower than those of tussah silk fiber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 750–758, 2001     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of non-woven mats from all-aqueous silk fibroin solution with electrospinning method

In the present study, we successfully prepared non-woven mats from stable regenerated silk fibroin aqueous solution at high concentration. Scanning electronic microscope (SEM) was used to observe the morphology of the fibers. The structure of the fibers was characterized using Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The mechanical tests were also performed. In the as-spun fibers, silk fibroin was present in a random coil conformation, the stress and strain at break were 0.82 MPa and 0.76%, respectively, while after methanol treatment, the silk fibroin was transformed into a β-sheet-containing structure, the stress and strain at break increased to 1.49 MPa and 1.63%, respectively. This study provided an option for the electrospinning of silk fibroin without using organic solvent or blending with any other polymers, which may be important in tissue engineering scaffold preparation.     

Molecular weight and secondary structure change in eri silk during alkali degumming and powdering

Changes in molecular weight and secondary structure of eri silk during alkali degumming and silk powdering were studied. An increase in silk degumming intensity, through increased alkali concentration, treatment temperature, and time, reduced the fibroin molecular weight and, therefore, the fiber tenacity, but at the same time, increased the β‐sheet fraction. These changes reduced the time required to mill the degummed silk fibers into fine powders. Mechanical forces used in wet attritor and air jet milling disturbed intermolecular packing along the direction of side chains, but the conformation remained essentially β‐sheet even in the sub‐micron silk particles. Dry milling drastically reduced molecular weight and changed the conformation of the fibroin chains. The rate of the spontaneous conformation transition in regenerated fibroin solution prepared from fibers and powders increased with a decrease in fibroin molecular weight, affecting the time fibroin solutions could be stored before gelling. Overall, the study showed that molecular weight and secondary structure of silk powders could be manipulated by suitably changing the degumming and milling conditions. It also suggests that wet media milling and air jet milling are better than dry media milling to prepare less degraded and more crystalline ultrafine silk particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Flow analysis of aqueous solution of silk fibroin in the spinneret of Bombyx mori silkworm by combination of viscosity measurement and finite element method calculation

Bombyx mori silk fibers possess outstanding mechanical properties in spite of being spun at room temperature and from the aqueous solution. Therefore, the mechanism of the structural transition has been studied with great attention, but still not be well understood. In this study the flow simulation of the silk fibroin aqueous solution using finite element method was performed on the basis of both the relationship between the viscosity and shear rate of the silk fibroin solution prepared from the silk gland, and the detailed structure of the spinneret including silk press part of the silkworm obtained from the optical micrographs. The viscosity of the silk fibroin solution decreased with power-law till the shear rate, about 1.5 s⁻¹ with increasing shear rate. Then the viscosity increased reversely which is speculated due to the fiber formation as a result of aggregation of the molecules. In the flow simulation analysis, the initiation site of the fiber formation was calculated by regulating the extrusion pressure. The fiber formation occurs in 550 μm from the spigot at 1 MPa and in 600 μm from the spigot at 50 MPa. The extrusion pressure in the range from 1 MPa to 50 MPa induces the fiber formation in the stiff plates (550-600 μm from the spigot), that is, the silk press part in the spinneret.     

Comparisons between silk fibroin nonwoven electrospun fabrics using aqueous and formic acid solutions

The objective of this study is to compare the spinnability, morphology, structure, mechanical properties, and cell compatibility of the silk fibroin nanofiber nonwoven electrospun fabrics using aqueous (AQ) solution and formic acid (FA) solution. The lower limit concentration was 5?wt% and 3?wt% of AQ solution and FA solution for electrospinning, respectively. The fiber diameter of electrospun fabric using FA solution was larger than that using aqueous solution at the same concentration. The secondary structure contents of silk fabrics were same between AQ and FA solutions. FA was remained in silk nanofibers, and the remained FA could be neutralized. Young’s modulus and cell adhesion on electrospun fabric using FA was lower than that using AQ solution. On the contrary, lower cell proliferation rate on electrospun fabric using FA was kept even after neutralization.     

Physical properties of 2-hydroxyethyl methacrylate-grafted silk fibers

This paper deals with the physical properties of silk fibers grafted with 2-hydroxyethyl methacrylate (HEMA). Both tensile strength and elongation measured in the dry and wet states gradually decreased with increasing weight gain. The initial modulus of the grafted silk fibers in the dry state sharply increased in the weight gain range of 0–16%, then decreased to a lower value than the reference untreated sample. The refractive indices parallel and perpendicular to the fiber axis decreased, though the former showed a steeper slope. Accordingly, birefringence and isotropic refractive index also decreased, suggesting a lower degree of crystallinity and molecular orientation of grafted silk fibers. DSC, TMA, and TGA curves of the HEMA-grafted silk fibers indicated an increased higher thermal stability of silk fibers due to the HEMA grafting. The dynamic mechanical measurements showed that the thermally induced molecular movement of both amorphous and crystalline domains of silk fibers was enhanced by HEMA grafting. X-ray diffraction curves, however, implied that the crystalline structure of the silk fibroin remained unchanged regardless of HEMA polymerization. The introduction of HEMA polymer in silk fibers was evidenced by the infrared spectra, exhibiting the absorption bands characteristic of either the grafted HEMA polymer and the fibroin molecules with ordered β structure. © 1993 John Wiley & Sons, Inc.     

Preparation and characterization of Bombyx mori silk fibroin and wool keratin

Silk and wool are well‐known protein‐based fibers. Their environmental stability, biocompatibility, and unique mechanical properties provide an important basis for using these natural proteins in biomedical applications. To use them as biomaterials in the form of fibers, films, or membranes, it is necessary to characterize these proteins in their solution and solid states because structural characteristics and morphological features have a great influence on the physical and mechanical properties of these new regenerated protein forms. Therefore, in the present study, silk fibroin and wool keratin were dissolved and their solution behaviors and secondary structures are analyzed and compared, using particle size distribution, molecular weight distribution (SDS‐PAGE), Fourier transform infrared, and X‐ray diffraction techniques. It was shown that keratin is more stable in solution and more amorphous in the solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4260–4264, 2006     

Silk I structure formation through silk fibroin self-assembly

Regenerated silk fibroin films are normally produced by increasing the Silk II structure (β-sheet content). In the present study, silk fibroin films were prepared by controlling the environmental temperature and humidity, resulting in the formation of silk films with a predominant Silk I structure instead of Silk II structure. Wide angle X-ray diffraction indicated that when the relative humidity was 55%, the silk films prepared were mainly composed of Silk I structure, whereas silk films formed on other relative humidity had a higher Silk II structure. Fourier transform infrared analysis (FTIR) results also conformed that the secondary structure of silk fibroin can be controlled by changing the humidity of the films formed process. Thermal analysis results revealed Silk I structure was a stable crystal, and the degradation peak increased to 320°C, indicating a greater thermal stability of these films formed under the 55% relative humidity conditions. Atomic force microscopy (AFM) results depicted silk fibroin in the fresh solution had many nanospheres existing with 20–50 nm diameters and mainly maintained a random coil structure without specific nanostructures. At the same time, it also illustrated the self-assembly process of silk fibroin in the aqueous solution without any human intervention. In addition, this present study also provided additional support for self-assembly mechanism of silk fibroin films formation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012