An analysis of deformation process on poly‐p‐phenylenebenzobisoxazole fiber and a structural study of the new high‐modulus type PBO HM+ fiber

This study is concerned with fiber structure of new high‐modulus type PBO fiber. Crystal modulus and molecular orientation change with stress was surveyed. Standard‐modulus type PBO (AS) fiber has hysteresis effect to applied stress while high‐modulus type PBO (HM) fiber shows reversible change. In order to raise actual PBO fiber modulus higher, nonaqueous coagulation process was adopted with conventional heat treatment. The fiber (HM+) so made gives 360 GPa in the Young's modulus and an absence of small‐angle X‐ray scattering pattern that is characteristic for aqueous‐coagulated PBO fiber with heat treatment (Zylon™ HM). The crystal structure form and crystal size for the HM+ fiber are the same as those of the HM fiber. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1605–1611, 2000     

Analysis of regenerated cellulose fibers with ionic liquids as a solvent as spinning speed is increased

In order to improve the spinning efficiency, the spinning experiments with cellulose/1-butyl-3-methylimidazolium chloride solution were done whilst increasing spinning speed. It was found that the tenacity and initial modulus of regenerated cellulose fibers increased but the elongation at break decreased slightly with increasing spinning speed at constant draw ratio. Further, the synchrotron wide-angle X-ray diffraction and small-angle X-ray scattering were carried out to illustrate the relationship between the structure and the mechanical properties. It was shown that the crystal orientation, crystallinity, amorphous orientation factor as well as orientation of the microvoids along the fiber increased with the spinning speed as the diameter of the microvoids in the fiber decreased. From the analysis of the spinline stress, it is clear that the spinline stress increased when both extruding and draw speed increased at constant draw ratio. This resulted in the improvement of supramolecular structure and mechanical properties of the regenerated cellulose fibers.     

An investigation into the relationship between internal stress distribution and a change of poly‐p‐phenylenebenzobisoxazole (PBO) fiber structure

This study concerns stress distribution induced by external force in individual poly‐p‐phenylenebenzobisoxazole (PBO) molecules in fiber. In reality, there are no fibers having an ideal structure (i.e., composed of infinitely long complete crystal elongated parallel to the fiber axis without defects that disconnect stress transfer in the crystal structure). Normally, real fiber structure has some structural incompletion, such as molecular ends, molecular misorientation, and density fluctuation (inhomogeneity) along the fiber axis. They play the role of heterogeneous stress distribution and reduction of fiber modulus in the fiber under tensile deformation. To carry out such analysis, meridional X‐ray diffraction peaks of the PBO fiber under stress were measured and discussed. Distribution of the diffraction peak profile (half‐height width of the diffraction profile) was especially considered. Change of the molecular orientation induced by external stress to the fiber was also estimated by measuring distribution of equatorial spots along the Debye ring. It was found that the distribution of the meridional diffraction spots became wider in the meridian, while the peak profile along the azimuthal direction became narrower as external stress was added for all three fibers. The degrees of response against stress came in this order: AS (180 GPa) > HM (280 GPa) > HM+ (360 GPa). Hosemann's analysis was adopted to analyze real crystallite size and disorder parameter (g) of crystallites. It indicated that the crystalline size does not vary but the ordering of periodicity in the crystal lattice starts to loosen as applied stress to the fiber is increased. The stress seems to affect only local micro regions in the crystal structure. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2901–2911, 2000     

Correlation of the minor-phase orientation to the flow-induced morphological transitions in thermotropic liquid crystalline polymer/PBT blends

Immiscible blends of thermotropic liquid crystalline polymers (TLCP) and a flexible polymer matrix show viscosity reductions and extensive fiber formation under certain flow conditions. Here we study these phenomena by directly examining the TLCP component's molecular orientation and the dispersed phase morphology. The rheology and morphology of blends of polybutylene terephthalate and a thermotropic copolyester (HX-8000 series, DuPont) at concentrations varying from 5 to 30 wt % of TLCP are characterized. It is found that the blends show viscosity reduction as well as stable fiber formation at shear rates dependent on the TLCP content. Wide-angle X-ray scattering is performed to measure the degree of molecular orientation of the TLCP phase. A deconvolution scheme isolates the scattering from the TLCP in the blends and a molecular model enables extracting an experimental orientation factor. It was found that a highly microfibrillated TLCP phase is coupled with an increase in the TLCP molecular orientation to values close to the pure TLCP at similar processing conditions. Further, the microfibrillated TLCP phase is found to be stable within the testing time. Current hypotheses about fiber formation in immiscible blends are tested against the experimental observations. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1769–1780, 1998     

聚丙烯腈基碳纤维中微孔洞的一维多取向小角X射线散射研究

应用一维多取向小角X射线散射(SAXS)方法研究了聚丙烯腈(PAN)基碳纤维中微孔洞的形态.结果表明,这些微孔洞沿纤维轴方向呈针状,并与纤维轴呈Φ=14°角的取向排列;微孔洞投影在碳纤维横截面上的平均半径R=1.14nm,投影在碳纤维轴向上的平均长度L=17.97nm.建立的一维多取向SAXS方法可以得到若干二维SAXS方法才能得到的微孔洞形态及分布信息等参数(如Φ和L),且在各种纤维的微孔洞或微纤维的表征方面具有一定的普适性.     

Deformation of lamellar structures: Simultaneous small- and wide-angle X-ray scattering studies of polyamide-6

Structural changes during tensile deformation in semicrystalline polymers are studied by the analysis of both small- and wide-angle X-ray scattering data from polyamide-6 fibers. The strain in the lamellar spacing is about the same as or higher than the fiber strain, suggesting that fiber elongation occurs by the deformation of the lamellar stack rather than slippage of the fibrils, especially during initial stages of elongation. The modulus of the lamellar structure is approximately 5 GN/m², and this is close to the fiber modulus, which is only 2–3% of the crystal modulus. Fiber modulus is, therefore, determined by the lamellar structure as much as by the interfibrillar oriented chain segments. The four-point small-angle X-ray scattering pattern in the relaxed fiber transforms reversibly into a two-point pattern under strain. The structures that correspond to these two patterns, the bistable states of the lamellae, coexist until fiber breakage. The structure that gives rise to the two-point pattern determines the ultimate strength of the fiber. Despite the small crystalline strain in the fiber direction, it is possible to follow the almost fully reversible changes in the orientation, size, and unit cell of the lamellar crystals. It is proposed that the appearance of the two-point pattern, the decrease in the lateral crystallite size, and the increase in the stack diameter are due to tilting of the lamellar surface caused by large-scale reversible strain in the interlamellar amorphous regions. This tilt is accomplished by slippage of the hydrogen-bonded sheets along the chain axis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 691–705, 2002     

Effects of ultra-high temperature treatment on the microstructure of carbon fibers

The microcrystalline structure and microvoid structure in carbon fibers during graphitization process(2300-2700 °C) were characterized employing laser micro-Raman scattering(Raman), X-ray diffraction(XRD), small angle X-ray scattering(SAXS), and high-resolution transmission electron microscopy(HR-TEM). The crystalline sizes(L_a, L_c) increased and interlayer spacing(d_(002)) decreased with increasing heat treatment temperature(HTT). The microvoids in the fibers grew up and contacted to the neighbors with the development of microcrystalline. In addition, the preferred orientation of graphite crystallite along fiber axis decreased and microvoids increased. The results are crucial for analyzing the evolution of microstructure of carbon fibers in the process of heat treatment and important for the preparation of high strength and high modulus carbon fibers.     

The synthesis,characterization, and crystal structures of poly(2,6‐naphthalenebenzobisoxazole) and poly(1,5‐naphthalenebenzobisoxazole)

The rigid‐rod polymers, poly(2,6‐naphthalenebenzobisoxazole) (Naph‐2,6‐PBO) and poly(1,5‐naphthalenebenzobisoxazole) (Naph‐1,5‐PBO) were synthesized by high temperature polycondensation of isomeric naphthalene dicarboxylic acids with 4,6‐diaminoresorcinol dihydrochloride in polyphosphoric acid. Expectedly, these polymers were found to have high thermal as well as thermooxidative stabilities, similar to what has been reported for other polymers of this class. The chain conformations of Naph‐2,6‐PBO and Naph‐1,5‐PBO were trans and the crystal structures of Naph‐2,6‐PBO and Naph‐1,5‐PBO had the three‐dimensional order, although the axial disorder existed for both Naph‐2,6‐PBO and Naph‐1,5‐PBO. Naph‐2,6‐PBO exhibited a more pronounced axial disorder than Naph‐1,5‐PBO because of its more linear shape. The repeat unit distance for Naph‐2,6‐PBO (14.15 Å) was found to be larger compared with that of Naph‐1,5‐PBO (12.45 Å) because of the more kinked structure of the latter. The extents of staggering between the adjacent chains in the ac projection of the crystal structure were 0.25c and 0.23c for Naph‐2,6‐PBO and Naph‐1,5‐PBO, respectively. Naph‐1,5‐PBO has a more kinked and twisted chain structure relative to Naph‐2,6‐PBO. The kinked and twisted chain structure of Naph‐1,5‐PBO in the crystal seems to prevent slippage between adjacent chains in the crystal structure. The more perfect crystal structure of Naph‐1,5‐PBO may be due to this difficulty in the occurrence of the slippage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1948–1957, 2006     

Thermal conductivity of high strength polyethylene fiber in low temperature

High strength polyethylene fiber (Toyobo, Dyneema® fiber, hereinafter abbreviated to DF) used as reinforcement of fiber‐reinforced plastics for cryogenic use has a high thermal conductivity. To understand the thermal conductivity of DF, the relation between fiber structure and thermal conductivity of several kinds of polyethylene fibers having different modulus from 15 to 134 GPa (hereinafter abbreviated to DFs) was investigated. The mechanical series‐parallel model composed of crystal and amorphous was applied to DFs for thermal conductivity. This mechanical model was obtained by crystallinity and crystal orientation angle measured by solid state NMR and X‐ray. Thermal conductivity of DF in fiber direction was dominated by that of the continuous crystal region. The thermal conductivity of the continuous crystal part estimated by the mechanical model increases from 16 to 900 mw/cmK by the increasing temperature from 10 to 150K, and thermal diffusivity of the continuous crystal part was estimated to about 100 mm²/s, which is almost temperature independent. The phonon mean free path of the continuous crystal region of DF obtained by thermal diffusivity is almost temperature independent and its value about 200 Å. With the aforementioned, the mechanical series‐parallel model composed of crystal and amorphous regions could be applied to DFs for thermal conductivity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1495–1503, 2005     

In situ polymerization and characterization of graphene oxide‐co‐poly(phenylene benzobisoxazole) copolymer fibers derived from composite inner salts

A facile and efficient strategy for preparing well dispersed graphene oxide (GO)‐co‐Poly(phenylene benzobisoxazole) (PBO) copolymer fibers was carried out by direct in situ polycondensation of composite inner salts. The composite inner salts were achieved to improve the dispersivity, solubility, reactivity, and interfacial adhesion of GO in PBO polymer matrix. The structure and morphology of GO‐co‐PBO copolymer fibers have been characterized. It was demonstrated that GO were covalently incorporated with PBO molecular chains and dispersed considerably well in PBO fiber even the GO reach to 3 wt %. Meanwhile, the tensile modulus, tensile strength and thermal stability of GO‐co‐PBO copolymer fibers increased considerably with GO. The mechanism and theoretical calculation of GO enhanced PBO fiber were also discussed. The main reasons for the improvement on performance of PBO fiber should be attributed to good dispersion GO in PBO matrix and covalent bonding networks at the interface between GO and PBO molecular chains. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Stress distribution in poly‐p‐phenylenebenzobisoxazole (PBO) fiber as viewed from vibrational spectroscopic measurement under tension. I. Stress‐induced frequency shifts of Raman bands and molecular deformation mechanism

To clarify the relationship between a molecular deformation mechanism and a high Young's modulus of poly‐p‐phenylenebenzobisoxazole (PBO), Raman spectra were measured for fibers subjected to a tensile stress along the chain axis. The stress‐induced frequency shift of the observed Raman bands could be reproduced reasonably by the normal‐mode calculation under a quasi‐harmonic approximation. The frequency position at zero stress and the shift factor of Raman bands were predicted for a PBO chain that agreed with the actually evaluated values. On the basis of these analyses, the molecular deformation mechanism of the PBO chain has been discussed in detail. The crystalline modulus of the PBO chain was calculated theoretically to be 458 GPa, in good agreement with the X‐ray observed value of 460 GPa. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1269–1280, 2002     

预氧化过程中张力对聚丙烯腈预氧化纤维微缺陷结构的影响

本文报道用同步辐射二维小角X射线散射(2D\|SAXS)研究预氧化过程中张力对PAN纤维缺陷的影响.     

Chain conformation of rod-like polymers in the melt: Small-angle neutron scattering of poly(benzoyl paraphenylene)

The chain conformation of a rigid rod polymer, poly(benzoyl paraphenylene), is determined in the melt using small-angle neutron scattering. The coherent scattering cross-section from blends of partially deuterated and hydrogenous poly(benzoyl paraphenylene) agree well with ideal rod scattering for q > 0.02 Å⁻¹, indicating that the polymer chains are highly extended. Comparison of the results to a single chain-scattering function for chains of arbitrary stiffness yield a persistence length of ca. 130 Å. Pure component scattering at the lowest scattering lengths indicate that the melt is not molecularly homogenous, but is comprised of domains, potentially reflecting localized groupings of chains with similar backbone orientation. Furthermore, this mesoscopic structure depends on the processing history of the polymer in the melt state. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2449–2459, 1998     

Assessment of thermal expansion coefficient of methylsilsesquioxane thin film

For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006     

Effect of short glass fiber on structure and viscoelastic behavior of olefinic polymers synthesized with metallocene catalyst

Several composites were prepared on the basis of an ethylene homopolymer and different copolymers of ethylene and 1‐hexene, synthesized with a metallocene catalyst, as matrices and a content of a 5 wt % of short glass fiber. The effect of the fiber incorporation on the structure and mechanical and viscoelastic behaviors was analyzed for the different samples. The glass fibers induced a slightly higher crystallinity, and the crystallite morphology significantly changed (long spacings and crystal orientation). The incorporation of fibers did not reinforce the different matrices under study at this low content; consequently, the mechanical parameters, such as Young's modulus, yielding stress, and microhardness, were lower in the composites as compared with those values found in the neat polyolefins. The location and apparent activation energies of distinct relaxation processes are also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1244–1255, 2003     

Morphological and mechanical properties of carbon nanotube/polymer composites via melt compounding

The mechanical properties and morphology of multiwall carbon nanotube (MWNT)/polypropylene (PP) nanocomposites were studied as a function of nanotube orientation and concentration. Through melt mixing followed by melt drawing, using a twin screw mini‐extruder with a specially designed winding apparatus, the dispersion and orientation of MWNTs was optimized in PP. Tensile tests showed a 32% increase in toughness for a 0.25 wt % MWNT in PP (over pure PP). Moreover, modulus increased by 138% with 0.25 wt % MWNTs. Transmission electron microscopy and scanning electron microscopy demonstrated qualitative nanotube dispersion and orientation. Wide angle X‐ray diffraction was used to study crystal morphology and orientation by calculating the Herman's orientation factor for the composites as function of nanotube loading and orientation. The addition of nanotubes to oriented samples causes the crystalline morphology to shift from α and mesophase to only α phase. Furthermore, the addition of nanotubes (without orientation) was found to cause isotropization of the PP crystal, and drawing was shown to improve crystal orientation through the orientation factor. In addition, differential scanning caloriometry qualitatively revealed little change in overall crystallinity. In conclusion, this work has shown that melt mixing coupled with melt drawing has yielded MWNT/PP composites with a unique combination of strength and toughness suitable for advanced fiber applications, such as smart fibers and high‐performance fabrics. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 864–878, 2006     

Axial X-ray scattering on high-performance polymeric fibers

High-temperature polymers were spum from liquid-crystalline solutions into fibers of superior thermal stability and mechanical properties. Fibers of two extended-chain polymers poly(p-phenyleneterephthalamide), PPTA, and poly-2,5-benzoxazole, ABPBO, as well as a rod-like polymer poly(p-phenylenebenzobisoxazole), PBO, were examined by axial x-ray scattering. Both wide-angle scattering and small-angle scattering were performed with CuKα radiation aiming along the fiber axis (c-axis) for structural information on the a-b lattice plane. In addition to previously reported lattice structure, the PPTA fibers (Kevlar® 29, 49, and 149) showed strong [004] and a [022] reflections suggesting that segments of the PPTA molecules were transverse to the fiber axis. This unique fiber structure is more prominent and the void content is less for the PPTA fibers with higher tensile modulus, (i.e., Kevlar® 149 > Kevlar® 49 > Kevlar® 29). Similar measurements on thermally annealed ABPBO and PBO fibers showed no [00l], [h0l], or [0kl] reflection indicative of a truly uniaxial molecular orientation. Evidence of microfibrillar order was discovered for the Kevlar® fibers and the ABPBO fiber. Results of conventional x-ray scattering on these fibers were compared and reconciled. © 1994 John Wiley & Sons, Inc.     

Macroscopic polymer analogues

Disordered fiber mats made of glass microfibers (GMF) were studied using small-angle light scattering (SALS), ultrasmall-angle X-ray scattering (USAXS), SEM, and optical microscopy. The morphological scaling of these materials in the micron scale was very similar to that of polymers in the nanometer scale. In some fiber mats, such as GMF, the structure is randomized at the time of formation, leading to a statistical analogy with the thermal randomization that occurs in nanometer-scale, high polymers. Analogues for the coil radius-of-gyration, persistence unit, and scaling regimes exist in such fiber mats and may be a useful feature both for modeling thermally equilibrated polymeric systems, as well as furthering the understanding of the physical properties of fiber mats through analogy with the theoretical understanding of thermally equilibrated polymeric systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3147–3154, 1998     

Effect of stereosequences on crystallinity and properties of zone‐drawn poly(vinyl alcohol) microfibrils

To effectively orient the molecular chains of novel syndiotactic poly(vinyl alcohol) (PVA) microfibrillar fiber (PVA fibril), a high‐temperature zone‐drawing method was adopted. The PVA fibrils were directly prepared from the saponification and in situ fibrillation without a spinning procedure. The maximum draw ratio of the PVA fibril increased with a decrease in the syndiotactic diad (r‐diad) content, indicating that the deformability of PVA molecules was lowered in higher syndiotactic PVA. Degree of crystal orientations up to 0.990 were achieved by stretching the PVA fibril with the r‐diad content of 65.1% and the original degree of crystal orientation of 0.902 at 250 °C close to its crystal melting temperature (T_m). When the same draw ratio was applied to the fibrils, a higher crystal orientation was achieved for the fibrils having higher syndiotacticity. Wide‐angle X‐ray data show that the longitudinal crystal sizes of drawn PVA fibrils were larger in higher syndiotacticities. The degree of crystal orientation, crystallinity, T_m, longitudinal crystal size, and tensile strength of the maximum drawn PVA fibril with a r‐diad content of 65.1% were 0.99, 0.97, 279 °C, 187 Å, and 4.66 N/tex, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1263–1271, 2001     

Mechanical properties and structure of the zone‐drawn poly(L‐lactic acid) fibers

The zone‐drawing (ZD) method was applied three times to the melt‐spun poly(L ‐lactic acid) (PLLA) fibers of low molecular weight (M_v = 13,100) at different temperatures under various tensions. The mechanical properties and superstructure of the ZD fibers were investigated. The resulting ZD‐3 fiber had a draw ratio of 10.5, birefringence of 37.31 × 10⁻³, and crystallinity of 37%, while an orientation factor of crystallites remarkably increased to 0.985 by the ZD‐1. The Young's modulus and tensile strength of the ZD‐3 fiber respectively attained 9.1 GPa and 275 MPa, and the dynamic storage modulus was 10.4 GPa at room temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 991–996, 1999