热致液晶高分子微纤的形貌特征和一个模量分析的方法

热致液晶高分子微纤的形貌特征和一个模量分析的方法益小苏，沈烈（浙江大学高分子科学与工程学系，杭州，３１００２７）关键词热致液晶高分子，原位复合，弹性模量，注塑由于主链型热致液晶高分子（ＬＣＰ）的高模量、高强度、易取向、低粘度等特性，当将这种高分子以较...     

Fiber property and structure development of polyester blend fibers reinforced with a thermotropic liquid‐crystal polymer

Ternary blend fibers (TBFs), based on melt blends of poly(ethylene 2,6‐naphthalate), poly(ethylene terephthalate), and a thermotropic liquid‐crystal polymer (TLCP), were prepared by a process of melt blending and spinning to achieve high‐performance fibers. The reinforcement effect of the polymer matrix by the TLCP component, the fibrillar structure with TLCP fibrils of high aspect ratios, and the development of more ordered and perfect crystalline structures by an annealing process resulted in the improvement of the tensile strength and modulus for the TBFs. An increase in the apparent crystallite size with the spinning speed was attributed to the development of larger crystallites and more ordered crystalline structures in the annealed TBFs. The birefringence and density of the TBFs increased with increasing spinning speed, the TBFs becoming more oriented and the crystal packing becoming more enhanced. The molecular orientation was an important factor in determining the tensile strength and modulus of the TBFs. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 395–403, 2004     

Drawing behavior and characteristics of laser‐drawn polypropylene fibers

Drawing behavior, flow drawing, and neck drawing, was studied for isotacticpolypropylene fibers in CO₂ laser drawing system, and the fiber structure and the mechanical properties of drawn fibers were analyzed. For a certain laser power, flow drawing of polypropylene (PP) was possible up to draw ratio (DR) 19.5. Though the drawing stress was very low, the flow‐drawn PP fiber exhibited oriented crystal structure and improved mechanical properties. On the other hand, neck‐drawing was accomplished from DR 4 to 12, with significant increase in drawing stress that enhanced the development of fiber structure and mechanical properties. Unlike PET, the drawing stress depends not only on the DR, but on irradiated laser power also. The 10–12 times neck‐drawn fibers were highly fibrillated. The fibers having tensile strength 910 MPa, initial modulus 11 GPa, and dynamic modulus 14 GPa were obtained by single‐step laser drawing system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 398–408, 2006     

A theory for the drawing of oriented crystalline polymers

The load-elongation behavior during the postneck drawing stage in the deformation of crystalline polymers is shown to be modeled quantitatively by an aligned short-fiber composite in which crystalline fibrils form the reinforcing phase in a matrix of less well-ordered material. Three modes of deformation are distinguished in the model and are shown to correspond to the observed loadelongation relations in polyethylene and polypropylene. The regions are (I) elastic–plastic crystals in an elastic matrix, (II) elastic–plastic crystals in an elastic–plastic matrix, (III) elastic crystals in an elastic–plastic matrix. A requirement of the theory is that the flow stress in the crystals is little affected by temperature whereas that in the matrix falls as the temperature rises. Expressions are given for stress in terms of the applied strain and the relevant parameters of the system: concentration of fibrils, length and diameter of fibrils, and elastic and yield properties of fibrils and matrix.     

Correlation between the tensile properties and network draw ratio of CO2‐laser‐heated drawn poly(ethylene terephthalate) fibers

Low‐orientation and amorphous poly(ethylene terephthalate) fibers were drawn continuously with heating by carbon dioxide (CO₂) laser radiation. The tensile properties were examined in terms of the birefringence and network draw ratio, which was estimated from the strain shift of true stress–strain curves. Two drawing forms, neck drawing with a draw efficiency (the ratio of the network draw ratio to the actual draw ratio) of about unity and flow drawing with a draw efficiency of about zero, were found to be stable in the continuous drawing process. Meanwhile, any draw‐efficiency value between zero and unity could be obtained in the batch‐drawing process. The object whose orientation was estimated by the network draw ratio differed from that estimated by birefringence. Two linear relationships were found, between the network draw ratio and tensile strength and between the birefringence and initial modulus. The true stress at breaking increased with the network draw ratio of the CO₂‐laser‐heated drawn fibers, and when the draw ratio exceeded 5.0, it became higher than that for batch‐drawn fibers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2322–2331, 2003     

Melt spinning and laser‐heated drawing of a new semiaromatic polyamide,PA9‐T fiber

Fibers of PA9‐T, a new semiaromatic polyamide containing a long aliphatic chain, were prepared by melt spinning. As‐spun fibers were subsequently drawn with a CO₂ laser‐heated drawing system at different draw ratios and various drawing velocities. On‐line observations of drawing points deciphered two drawing states; namely, flow drawing and neck drawing, over the entire range of drawing. Drawing stress revealed that flow drawing is induced by slight drawing stress under a low draw ratio up to 3, and neck drawing is induced by relatively high drawing stress under a higher draw ratio. The effect of drawing stress and drawing velocity on the development of the structure and properties has been characterized through analysis of birefringence, density, WAXD patterns, and tensile, thermal, and dynamic viscoelastic properties. For the neck‐drawn fibers, almost proportional enhancements of crystallinity and molecular orientation with drawing stress were observed. The flow‐drawn fibers have an essentially amorphous structure, and birefringence and density do not always have a linear relation with properties. The fibers drawn at high drawing speed exhibit improved fiber structure and superior mechanical properties. The maximum tensile strength and Young's modulus of PA9‐T drawn fibers were found to be 652 MPa and 5.3 GPa, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 433–444, 2004     

Effects of cellulose nanofibrils on the structure and properties on PVA nanocomposites

A green method—joint mechanical grinding and high pressure homogenization—was used to defibrillate paper pulp into nanofibrils. The prepared cellulose nanofibrils (CNF) were then blended with PVA in an aqueous system to prepare transparent composite film. The size and morphology of the nanofibrils and their composites were observed, and the structure and properties were characterized. The results showed that CNFs are beneficial to improve the crystallinity, mechanical strength, Young’s modulus, T _g and thermal stability of the PVA matrix because of their high aspect ratio, crystallinity and good compatibility. Therefore, nano cellulosic fibrils were proven to be an effective reinforcing filler for the hydrophilic polymer matrix. Moreover, the green fabrication approaches will be helpful to build up biodegradable nanocomposites with wide applications in functional environmentally friendly materials.     

Comparative study of pineapple leaf microfiber and aramid fiber reinforced natural rubbers using dynamic mechanical analysis

Natural fiber is often considered inadequate for high performance reinforcement of polymer matrix composites. However, some natural fibers have relatively high mechanical properties with modulus close to that of high-performance synthetic fibers. Since the reinforcing efficiency of a short fiber is determined not only by the fiber modulus, but also by other physical properties such as the length to diameter ratio. Here it is shown, for the first time, that pineapple leaf fiber, whose modulus is somewhat lower than that of aramid fiber, can be used to reinforce natural rubber more effectively than aramid fiber. The situation was achieved by breaking down the fiber bundles into the constituent microfibers to gain very high aspect ratio. Comparisons were made at fiber contents of 2, 5 and 10 parts (by weight) per hundred of rubber (phr) using dynamic mechanical analysis over a range of temperature. The results reveals that at temperature below the glass transition of the matrix rubber and low fiber contents of 2 and 5 phrs, aramid fiber displays slightly better reinforcement efficiency. At high temperatures of 25 and 60 °C and high fiber content of 10 phr, pineapple leaf microfiber clearly displays higher reinforcement efficiency than does aramid fiber. Surface modification of the fiber by silane treatment provides a slight improvement in reinforcing efficiency.     

热塑性树脂的增强：从原位复合材料到原位混杂复合材料

综述了两类增强的热塑性树脂的基本方面。一类是由原位形成的热致液晶聚合物微纤增强的原位复合材料。从实验上研究了获得有效增强效果的两个关键因素；致热液晶聚合物的基体树脂中的成纤，以及在液晶聚合物与基体树脂不相容共混物中的增容作用。另一类是由作者发明的原位混杂复合材料，这一类材料是用直径在两个数量级上的纤维和原位形成的微纤混杂增强的。     

Thermal behavior of drawn acrylic fibers

The effect of stretching on the thermal behavior of acrylic fibers was investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). In air atmosphere, the peak temperature of the dynamic DSC thermogram was significantly lowered from 289 to 273 °C when the gel fibers (undrawn) were drawn to a draw ratio of 11.2. However, the initiation temperature was unchanged at 202 °C. The shoulder in the region of 310–380 °C was gradually converted to a sharp peak during the drawing process. However, the dynamic DSC in nitrogen atmosphere did not change in all cases. In air atmosphere the total heat liberated, ΔH, for gel fiber was 851 J g^?1. However, upon drawing to 11.2, ΔH increased to 1580 J g^?1 showing an increase in the total chemical changes. An intimate relationship of chemical changes during the heating process was observed with FTIR of heated samples at various temperatures. The initiation of a DSC exotherm in air begins with nitrile cyclization, and subsequently dehydrogenation was initiated between 220 and 260 °C. An increase in the X‐ray orientation factor and sonic modulus gave a correlation between the stretching draw ratio and crystalline/overall molecular orientation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2949–2958, 2003     

Effects of Compositions and Processing Variables on Barrier and Mechanical Properties of Liquid Crystalline Polymer/Polyethylene Blend Films

Cast films of liquid crystalline polymer (LCP) and low density polyethylene (LDPE) blends have been produced and investigated. Effects of LCP content and processing parameters, i.e., processing temperature profile, screw speed, and post-die drawing, on morphology and O₂ barrier property are presented. Increasing processing temperature and LCP content tend to enhance aspect ratios (L/D) of the LCP dispersed phase and at the same time influencing LCP structure. These effects are clearly observed when LCP content is increased from 10 % to 30 % by wt. At high temperature profiles, LCP morphologies are presented in a more or less ‘ribbon’ or ‘tape’ like structure together with a common LCP fibrillar structure. Films of 10% and 30% LCP produced at two optimum temperature profiles show a noticeable proportion of LCP tape-like structure and interestingly high barrier properties of ∼1.6 and 5.5 times that of the neat LDPE films. High barrier characteristics of such LCP/PE blend films are indicated by low oxygen transmission rate values. Apart from processing temperature effect, increases of screw speed result in films having smaller aspect ratios for both LCP fibers and ribbons; films also exhibit poorer barrier and mechanical properties. However, post-die drawing clearly demonstrates a positive effect in improving aspect ratios of the LCP domains and the resulting films' moduli. Effects of post-die drawing on enhancing films' barrier properties become more pronounced at high LCP content. By comparing with the neat LDPE film (30 μm thick) having modulus of ∼180 MPa and OTR of ∼11000 cc/m².day, the developed LCP/PE films containing 30 wt% LCP show remarkably high modulus values of ∼1100 MPa with low OTR of ∼2000 cc/m².day.     

Biocomposites based on Alfa fibers and starch‐based biopolymer

Biocomposite materials based on Alfa cellulose fibers (esparto grass plant) as reinforcing element and starch‐based biopolymer matrix were prepared and characterized in terms of mechanical performance, thermal properties, and water absorbance behavior. The fibers and the matrix were first mixed in the melted state under mechanical shearing using a plastograph and the obtained composites were molded by injection process. The tensile mechanical analysis showed a linear increase of the composite flexural and tensile modulus upon increasing the fiber content, together with a sharp decrease of the elongation at break. The fibers′ incorporation into the biopolymer matrix brings about an enhancement in the mechanical strength and the impact strength of the composite. Dynamic mechanical thermal analysis (DMTA) investigation showed two relaxations occurring at about ?30 and 35°C. The addition of Alfa fibers enhanced the storage modulus E′ before and after T_α, which is consistent with the reinforcing effect of Alfa cellulose fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics

The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.     

Orientation behavior of high-modulus polyoxymethylene produced by microwave heating drawing

The orientation behavior of high-modulus polyoxymethylene tapes produced by tensile drawing with microwave heating has been investigated over the draw ratio range 10–29. Young's modulus E increases monotonically with draw ratio λ and reaches 55 GPa. The volume fraction of taut tie molecules (TTMs) in the amorphous phase has been estimated by using a Takayanagi model for oriented tapes. The increase in E at draw ratios of less than 10 is mainly due to the increase in crystalline orientation (crystalline orientation function, 0.00 → 0.99). The increase in E at draw ratios of more than 10 is due to the increase both in crystallinity (volume-fraction crystallinity, 0.84 → 0.95) and in TTM (TTM fraction, 0.14 → 0.40). The maximum Young's modulus obtainable by this method of drawing is estimated to be ca. 72 GPa from the relation between 1/E and 1/λ².     

Hydration in semicrystalline polymers: Small-angle neutron scattering studies of the effect of drawing in nylon-6 fibers

Water absorbed by nylons appears to be partitioned into interlamellar and interfibrillar spaces. The amount of water in the interfibrillar region remains essentially unchanged with increasing draw ratio, whereas that in the interlamellar regions decreases with draw ratio; the latter accounts for the decrease in the water uptake in the drawn fibers. These results suggest that the amount of the amorphous material in the interfibrillar regions remains unchanged during drawing, and the increase in the crystallinity during drawing results from the incorporation of the amorphous chain segments in the interlamellar regions into the crystalline lamellae. Further, the interfibrillar water is more tightly bound than the interlamellar water. The length of the longitudinal channels into which water diffuses is about the same as that of the fibrils, and increases from ca. 1500 to 2000 Å upon drawing. The longitudinal channels are highly oriented even in undrawn fibers, and their misorientation increases from 5° to 15° upon drawing. These channels can be described as surface fractals of dimension 3.4–3.6. © 1994 John Wiley & Sons, Inc.     

Microstructure and mechanical properties of hot‐air drawn poly(ethylene terephthalate) fibers

Hot‐air drawing method has been applied to poly(ethylene terephthalate) (PET) fibers in order to investigate the effect of strain rate on their microstructure and mechanical properties and produce high‐performance PET fibers. The hot‐air drawing was carried out by blowing hot air controlled at a constant temperature against an as‐spun PET fiber connected to a weight. As the hot air blew against the fibers weighted variously at a flow rate of about 90 ℓ/min, the fibers elongated instantaneously at a strain rate in the range of 2.3–18.7 s⁻¹. The strain rate in the hot‐air drawing increased with increasing drawing temperature and applied tension. When the hot‐air drawing was carried out at a drawing temperature of 220°C under an applied tension of 27.6 MPa, the strain rate was the highest value of 18.7 s⁻¹. A draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest stain rate had a birefringence of 0.231, degree of crystallinity of 44%, tensile modulus of 18 GPa, and dynamic storage modulus of 19 GPa at 25°C. The mechanical properties of fiber obtained had almost the same values as those of the zone‐annealed PET fiber reported previously. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1703–1713, 1999     

Modeling the mechanical properties of highly oriented polymer films: A fiber/gel composite theory approach

Controlling the extent of orientation is of great interest in polymer processing and is effected by the choice of polymer, the fabrication technique and the processing conditions. Understanding the crystalline transitions that form highly oriented fibrils is necessary for modeling the changes in physical properties, relative to degree of orientation. A model is proposed to describe the mechanical properties of drawn semicrystalline polymer films based on structural transitions. With a minimal amount of experimental data (requiring testing on only two drawn films samples), this model can be used to predict film properties. These properties include the critical and maximum draw ratios, the moduli at the maximum draw ratio, the moduli of the fiber, the modulus of the nonfibrous gel relative to draw ratio, the volume fraction of fibers, and the rate of fibrillation. Where high degrees of uniaxial orientation are required, the polymer is typically drawn in the solid state, meaning the polymer is stretched in a single direction at temperatures below the melting point. During this process, pre‐existing crystallites are transformed into fiber‐like structures with large aspect ratios. The presence of these rigid asymmetric structures significantly enhances the moduli and break strength of the polymer. This work presents a model that describes the formation of fiber‐like structures. The volume fraction of fibers is predicted to be linear in draw ratio. The derived relationship between volume fraction of fibers and draw ratio can then be used for the prediction of the various properties of the oriented film. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 607–618, 2008     

Isolation and characterization of cellulose nanofibers from banana peels

Cellulose nanofibers were isolated from banana peel using a combination of chemical treatments, such as alkaline treatment, bleaching, and acid hydrolysis. The suspensions of chemically treated fibers were then passed through a high-pressure homogenizer 3, 5, and 7 times, to investigate the effect of the number of passages on the properties of the resulting cellulose nanofibers. The cellulose nanofibers isolated in this study had a dry basis yield of 5.1 %. Transmission electron microscopy showed that all treatments effectively isolated banana fibers in the nanometer scale. The micrographs of the process steps used to isolate the nanofibers revealed gradual removal of amorphous components. Increasing number of passages in the homogenizer shortened the cellulose nanofibers while furnishing more stable aqueous suspensions with zeta potential values ranging from ?16.1 to ?44.1 mV. All the samples presented aspect ratio in the range of long nanofibers, hence being potentially applicable as reinforcing agents in composites. X-ray diffraction studies revealed that homogenized nanofiber suspensions were more crystalline than non-homogenized suspensions. Fourier transform infrared spectroscopy confirmed that alkaline treatment and bleaching removed most of the hemicellulose and lignin components present in the banana fibers. Thermal analyses revealed that the developed nanofibers exhibit enhanced thermal properties. In general, the nanoparticles isolated from the banana peel have potential application as reinforcing elements in a variety of polymer composite systems.     

热致液晶聚合物微纤与碳纤维对聚醚砜的混杂增强

热致液晶聚合物微纤与碳纤维对聚醚砜的混杂增强张洪志王育立何嘉松（中国科学院化学研究所工程塑料国家重点实验室北京１０００８０）关键词热致液晶聚合物，碳纤维，混杂复合材料由两种或两种以上纤维增强同一种基体所得到的混杂纤维复合材料，不仅保留了单一纤维...     

Mechanical properties of ultra-oriented polyethylene

Semicrystalline polymers generally exhibit moduli well below their theoretical limit due to chain folding and to lack of crystal alignment. Modulus increases attainable through standard drawing procedures are limited by sample fracture before large draw ratios are reached. Using an Instron capillary rheometer which allowed a draw ratio of > 300, transparent polyethylene strands of unusually high c-axis orientation have been produced by a combination of pressure and shear. The virtually perfect crystalline orientation and evidence for extended chains confirm that a significant improvement in modulus can be realized by this technique. The dynamic tensile storage modulus was measured by Vibron over the temperature range ?160°C to +120°C. Room-temperature moduli were 7 × 10¹¹ dyne/cm², higher than any reported values for drawn polyethylene. Values also remained above 10¹¹ dyne/cm² even at 120°C. The moduli and morphological data have been related by a model consisting of an extended-chain component in paralled with a conventional drawn morphology. Experimental and calculated moduli are compared and related to available theory.