Dual polymer bonding of thermoplastic composite structures

This paper describes a process that facilitates fusion bonding of thermoplastic composite components without the need for complex fixtures and without disrupting the fiber alignment in the component laminates. The dual polymer bonding process, Thermabond, requires that an interlayer polymer be fused to the surface of each laminate prior to bonding. The characteristics of the interlayer polymer allow for joining of the components at a temperature below the softening/melting point of the reinforced polymer in the composite laminates. This leads to significant processing advantages without significant loss in mechanical performance. Discussions of resin compatibility, the effect of process conditions on mechanical performance, and the application of the APC-2/PEI Thermabond system to various structural components are included.     

In-situ composites: Evaluation of the adhesion between the thermoplastic matrix and the fibers of liquid crystalline polymer

Mechanical properties of fiber reinforced composites depend on the formation of stable adhesive bonds between the constituents. In order to evaluate quantitatively the adhesion between liquid crystal polymer (LCP) fibers and a thermoplastic matrix of polycarbonate, the single fiber composite test (SFC), utilized for testing glass or carbon fiber composites, has been used. Neither chemical nor physical interaction has been found: the PC and LCP phases are completely incompatible. However, a mechanical friction between PC and LCP was observed during the drawing of the sample when the neck of the matrix started.     

Preparation and characterization of liquid crystal composite film using photosensitive hydrophilic matrix

Methoxybenzylidene n-butylaniline (MBBA) and ethoxybenzylidene n-butylaniline (EBBA) liquid crystal were synthesized. To investigate the applications of hydrophilic monomers and polymers on the field of liquid crystal composite film, 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (Aa) were selected as monomers for the polymer matrix. To prepare the liquid crystal composite film, MBBA, EBBA, and commercial liquid crystals ZLI-2444, 2452, 2459, and BDH-E7 were mixed with HEMA, Aa, and photosensitive materials and then irradiated by UV light. The electro-optical behavior and the microstructure of the liquid crystal composite films were investigated by He-Ne laser and scanning electron microscopy, respectively. The effects of UV light irradiation and monomer ratio on the electro-optical behavior of liquid crystal composite films were investigated. The reproducibility and storage stability of the liquid crystal composite films were investigated. © 1996 John Wiley & Sons, Inc.     

Induced orientational behavior of liquid crystal polymer by carbon fibers

Experimental results are presented that show that the structure of carbon fibers induces molecular orientation of liquid crystal polymers. X-ray diffraction data are used to demonstrate final collinearity of the polymer molecular axis and carbon fiber axis independent of fabrication approaches or prefabrication orientation of the polymer relative to the carbon fiber direction. The final degree of polymer molecular orientation approximately equals the degree of carbon basal plane orientation within the carbon fiber.     

Polymer crystal silverware: a fast method for the prediction of polymer crystal structures

Summary A method is presented for the fast prediction of polymer crystal structures. From a stable helical conformation of the polymer chain well packed three dimensional periodic starting structures are generated using an adapted version of M. Blanco's Molecular Silverware algorithm. These structures are then energy-minimised using classical molecular mechanics methods. The method only requires a rough estimate of the crystalline density. No information about crystal class, space group or cell parameters is necessary. Using this method, possible crystal structures of poly(ethylene ketone), Nylon-6,6 and poly(ethylene terephthalate) are calculated. Both the - and -structures of poly(ethylene ketone) are correctly predicted. For Nylon-6,6 the lowest-energy structure obtained corresponds to the experimental -structure. For poly(ethylene terephthalate) a large number of structures are generated using the algorithm. Besides the experimental structure four structures are found with a lower energy than the experimental structure.     

Semicrystalline thermoplastic polyimide + polymer liquid crystal blends: Nonisothermal calorimetry and thermogravimetry

Blends of a thermoplastic polyimide (TPI) and a polymer liquid crystal (PLC) were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PLC enhances orientation in the system and lowers the crystallization temperature-—a manifestation of the channeling effect predicted theoretically (38). The degradation studies show high temperature stability of all blends with the degradation onset consistently above 520°C. The onset decreases with PLC concentration but reaches a plateau above 30 wt% PLC when the PLC-rich islands are formed. The amount of moisture absorbed decreases with the PLC concentration while the moisture does not affect the degradation of the samples significantly. A phase diagram is constructed for the PLC + TPI blends from the DSC and TGA data. A comparison of amorphous and semicrystalline TPI and the characterization of amorphous TPI + PLC blends will be reported later.     

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal (PSLC) film is a relatively novel electro-optical material, which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal. In this paper, the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation. The effects of liquid crystal concentration, curing time, monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated. The results show that the transmittance in the OFF state (T _OFF) increased with the liquid crystal concentration, but the driving voltage decreased. T _OFF was also influenced by the curing time. Furthermore, when polyimide was used as alignment layer, the films prepared from the bifunctional monomer shows a higher T _OFF, while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks. __________ Translated from Polymer Materials Science and Engineering, 2008, 24(1): 63–66 [译自: 高分子材料科学与工程]     

Metallization of a liquid crystal polymer by PVD using a nickel interlayer

In this paper metallization of a liquid crystal polymer (LCP) substrate by physical vapor deposition (PVD) is described. Pretreatment of LCP substrates with oxygen-containing plasma improves the adhesion strength between the PVD copper layer and substrate. When a nickel interlayer was used, the adhesion was improved further. Still higher adhesion was also achieved with appropriate bias used during deposition of the nickel interlayer by PVD. Even after 1000 cycles of thermal shock the adhesion strength of Cu/Ni on LCP pretreated with oxygen plasma was still high.     

Thermal expansivity and thermal conductivity of amorphous thermoplastic polyimide and polymer liquid crystal blends

Linear thermal expansivities α_L and thermal conductivities of polyimide (TPI) and polymer liquid crystal (PLC) blends were studied. The glass transition temperatures T_g of our amorphous TPI and the PLC are, respectively, 240 and 220°C. The addition of the PLC induces orientation through the channeling process, as predicted by an extension of the Flory statistical‐mechanical theory of PLCs (27). Channeling was observed at PLC concentrations as low as 5 wt%. Thermal conductivity decreases with the addition of the PLC to the TPI. The anisotropic expansivity of the blends shows a strong dependence on PLC concentration and orientation direction. The pure PLC shows a maximum on the along‐the‐flow expansivity vs. temperature curves and also negative α_L values. TPI addition moves the expansivities to positive values, but the maximum persists, even for 5% PLC only.     

Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix

This study investigates deformation of a thermotropic liquid crystalline polymer (TLCP) in different die geometries. Blends of aTLCP with a thermiplastic elastomer of EPDM were made in a twin-screw extruder. Morphological observation of the extruded blends demonstrates the complimentary effect of shear in the die exit on dispersed phase deformation and fibril formation. Shear strain can affect fibril formation for a relatively large dispersed phase in the region close to the die wall. However, the main role of shearing is in breaking up the larger particles and initial polydomain structure. A strong elongational deformation on the blended melt after the die exit is required, and fine microfibrils normally obnserved in in situ composites were not easily formed by shear deformation only in the die.     

Bistable light scattering effects in a (side chain liquid crystalline polymer)/(low molecular weight liquid crystal) composite and in a ferroelectric liquid crystalline polymer

The electro-optical effects and aggregation states of liquid crystalline polymer (LCP)/ low molecular weight liquid crystal (LC) composite and ferroelectric liquid crystalline copolymer (FLCP) have been investigated. The nematic LCP was observed to be miscible with the nematic LC over wide ranges of concentration and temperature. The binary mixture showed an induced smectic phase in the range of 80/20-20/80 mol%. The electro-optical effects of the LCP/LC composite in an induced smectic phase could be classified into the turbid (light- scattering) and the transparent states upon application of AC and DC electric fields, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal in the chiral smectic C phase of FLCP. The reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of DC and AC electric fields, respectively. Both transparent and light-scattering states of the LCP/LC composite and the FLCP could be maintained, even after the electric field had been turned off (memory effect). The bistable effects of LCP/LC composite and FLCP are opposite under the same conditions. A novel type of electro-optical effect on light scattering was obtained for liquid crystalline polymer in the smectic states.     

Rheological behavior of a semirigid liquid crystal polymer

The rheological behavior of liquid crystal polymers is still far from completely clarified from both experimental and theoretical points of view. In this paper, the shear flow and the non-isothermal elongation flow behavior of a semirigid liquid crystal copolyester is discussed. The viscosity strongly decreases when the test temperature is increased above the crystal-nematic transition temperature; below this temperature the viscosity is very high. The thermal history strongly affects the shear viscosity. The elongational flow behavior depends also on temperature. Above the crystal-nematic transition temperature and the mesophase is easily spinnable, whereas below this temperature, the spinnability is very poor.     

Solution spinning of a semirigid chain polymer forming ultrahigh modulus fibers

Single filaments of the polyterephthalamide of p-aminobenzylhydrazide (X-500) were prepared by spinning X-500 solutions in dimethyl sulfoxide (DMSO) using water as a coagulating agent. The polymer is known for its ability to develop ultrahigh modulus fibers and for having a semirigid chain conformation with a persistence length of ～50 Å in DMSO. In the latter solvent, molecular rigidity appears to be just below that required for spontaneous formation of a nematic phase. The orientation of the fibers was performed in three different stages: during coagulation (I), in the washing bath following coagulation (II), and during postspinning treatments (III). Corresponding mechanical properties were determined. The results indicate that high elastic modulus (15 GPa) already appears during step I at very moderate pulloff ratios. Therefore, considerable orientation had already occurred in the flowing solution. Further increase of fiber orientation yields a large increase of modulus (from 22 to 67 GPa) during solid-state deformation (step III). The orientation of the flowing solution was monitored by viscosity and birefringence measurements. The results are discussed in terms of orientation due to elongational and shear flow and, possibly, a flow-induced transition to a nematic phase in the concentrated solution in which chain entanglement is shown to occur.     

Surface alignment of ferroelectric liquid crystals using side chain ferroelectric liquid crystal polymer

New surface alignment material for surface stablized ferroelectric liquid crystal displays (SSFLCDs) is investigated. Side chain ferroelectric liquid crystal polymer (SCFLCP) such as Poly{methyl 4-[[[S-(-)-2-methyl-1-butoxy]carbonyl] phenyl ]4-hexyloxybenzoyl}Siloxane was used as the alignment layer which resulted in good uniform alignment of FLC molecules without zig-zag defects. However, RN-715 polyimide alignment layer showed random alignments with some zig-zag defects in the SSFLC cells. After the field stablization of±20 V AC, the typical stripe-shaped patterns appeared. Good electro-optical performance was observed by using SCFLCP.     

Solution processing of composite fibers containing rodlike and thermoplastic polymers

The solution processing and mechanical properties made from blends of the rodlike polymer poly(p-phenylene benzobisthiazole) with either poly(ether ether ketone) or nylon 6,6 is described. The concentration dependence of the isotropic-nematic phase transition for solutions of these polymers in methane sulfonic acid is in qualitative agreement with a theory of Flory. The mechanical properties of fibers that were wet spun from isotropic solutions of poly(ether ether ketone) and poly(p-phenylene benzobisthiazole) are very sensitive to the concentration of the spinning solution. Fibers spun at concentrations near the isotropic-nematic phase boundary have poor mechanical properties, resulting from phase separation during coagulation. However, when the solution concentration is significantly below the critical value, stiff and strong fibers are produced. In contrast, when nylon 6,6 is used as the thermoplastic component, the mechanical properties are good and are insensitive to the solution concentration. We attribute the solution concentration effects to two factors. The first is the difference in the solubility of poly(ether ether ketone) and nylon 6,6 in methane sulfonic acid-water mixtures. The second is the connectivity of the nematic phase, which also depends on concentration and has a major impact on the mechanical properties of the resulting fiber.     

Coating carbon fibers with a thermoplastic polyimide using aqueous foam

Many techniques have been developed to coat carbon fibers with thermoplastic resins to form a prepreg. These techniques include melt impregnation and solution/slurry coating. The applicability of these techniques, however, may be restricted by high melt viscosities or significant drying times. Recent emphasis has been towards a dry powder coating technique using a fluidized bed. This technique may be limited by difficulties in fluidization of the polymer powders. To overcome these difficulties, a technique has been developed to continuously coat carbon fibers with thermoplastic resins using aqueous foam as a carrier medium. The polymer is slurried in a surfactant solution, into which air is dispersed using a foam-generating device. A predetermined amount of this foam is then applied to a moving carbon fiber tow using a foam application unit. The tow is then pulled through ovens where the foam is collapsed and the power fused to the fibers. Other aspects that are addressed include the stability of foams in the presence of powders, the mechanical properties of the composites formed using foam prepregging, and the effect of surfactant on composite properties.     

新型聚合物管件成型方法——挤出成型过程

通过自行设计的挤出成型实验台,将聚氯乙烯管材通过挤出成型制备三通管件,并研究了挤出成型过程中工艺参数与成型制品结构之间的关系。