Mechanical performance of ternary in situ polycarbonate/poly(acrylonitrile‐butadiene‐styrene)/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/poly(acrylonitrile‐butadiene‐styrene) (ABS)/liquid crystalline polymer(LCP) composites were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix of composite specimens was PC/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these composites. The tensile, dynamic mechanical, impact, morphology, and thermal properties of the composites were studied. Tensile tests showed that the tensile strength of the PC/ABS/LCP composite in the longitudinal direction increased markedly with increasing LCP content. However, it decreased slowly with increasing LCP content in the transverse direction. The modulus of this composite in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PC/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the composites in both longitudinal and transverse direction decreased with increasing LCP content up to 15 wt %; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the composites tended to increase with increasing LCP content. Scanning electron microscopy observation and DMA measurement indicated that the additions of epoxy and MA copolymer to PC/ABS matrix appeared to enhance the compatibility between the PC and ABS, and between the matrix and LCP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2274–2282, 1999     

Thermotropic polyester amide-carbon fiber composites

Liquid crystal polymers (LCP) have been developed for the first time as a thermoplastic matrix for high-performance composites. A successful melt impregnation method has been developed that results in the production of continuous carbon fiber (CF)-reinforced LCP prepreg tape. Subsequent layup and molding of prepreg into laminates has yielded composites of good quality. Tensile and flexural properties of LCP-CF composites are comparable to those of epoxy-CF composites. LCP-CF composites have better impact resistance than the latter, although epoxy-CF composites possess superior compression and shear strength. LCP-CF composites have good property retention until 200°F (67% of room temperature value). Above 200°F, mechanical properties are found to decrease significantly. Experimental results indicate that the poor compression and shear strength may be due to the poor interfacial adhesion between the matrix and carbon fiber.     

Injection molding of PC/PBT/LCP ternary in situ composite

A liquid crystalline polymer (LCP), Vectra B950, reinforced polycarbonate (PC) 60 wt%/polybutylene terephthalate (PBT) 40 wt% blend was studied using the injection molding process. Morphology and mechanical properties of ternary in situ LCP composites were investigated and compared with binary polycarbonate/Vectra B950 LCP composites. Good in situ fibrillation of LCP was observed in the direct injection-molded LCP composites. Preliminary results of this work indicate that addition of PBT improves skin-core distribution of LCP microfibrils in the matrix and also enhances adhesion between the matrix and Vectra B950, which contains terephthalic acid. The PC/PBT/LCP ternary system also exhibits lower viscosity than the PC/PBT blend and pure LCP. In a ternary system with 30 wt% of Vectra B950, tensile modulus and strength increase approximately threefold and twofold, respectively. The rule of mixtures (ROM) for continuous reinforcement can accurately represent the strengthening effects for the ternary LCP in situ composites. Generally, LCP reduces the ductility and impact strength of the thermoplastic blends; however, the relative loss is less in the ternary system than in the binary system.     

Properties of ternary in situ polycarbonate/polybutylene terephthalate/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/polybutylene terephthalate (PBT)/liquid crystalline polymer (LCP) composites were prepared by injection molding. The liquid crystalline polymer used was a versatile Vectra A950. The matrix of composite was composed of PC/PBT 60/40 by weight. A solid epoxy resin (bisphenol type‐A) was used as a compatibilizer for the composites. Dynamic mechanical analysis (DMA) showed that epoxy resin was effective to improve the compatibility between PC and PBT, and between PC/PBT and LCP, respectively. Tensile tests revealed that the stiffness of composites shows little change with the LCP content up to 10 wt %. Above this concentration, the stiffness tended to increase with increasing LCP content. Furthermore, the tensile strengths appeared to increase with increasing LCP content, and their values were close to those predicted from the rule of mixtures. Scanning electron microscopic examination showed that LCP ribbons and short fibrils were developed in the composites containing LCP content ≤10 wt %. However, fine and elongated fibrils were formed in the skin and core sections of the composites when the LCP content reached 25 wt % and above. Thermogravimetric analysis indicated that the thermooxidative stability of the PC/PBT 60/40 blend tended to improve with increasing LCP content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1827–1835, 1999     

Fiber reinforcement and fracture resistance of PC/PBT/LCP ternary in situ composite

The microstructures, mechanical properties, and fracture toughness of LCP (Vectra B950) reinforced PC/PBT blend with a 60/40 weight ratio have been studied. LCP of varying concentrations were investigated as rigid fillers in matrices of multiphase polymer blends. In this study, differences in microstructures and morphology between samples of two thicknesses (4 mm thick and 6 mm thick) and two geometries (dumbbell and rectangular) were compared using scanning electron microscopy (SEM). Given identical processing conditions, fibrous LCP structures were evident in the 4-mm-thick injection molded, dumbbell-shaped samples, whereas the 6-mm-thick rectangular samples displayed spherical dispersion of LCP aggregates that embrittled the preblended ductile matrix. Tensile properties of the dumbbell specimens showed superior strengthening and stiffening whereby the tensile strength increased twofold and the modulus increased fourfold. Plane strain fracture toughness was slightly enhanced as the LCP content increased because of the fiber strengthening effect but the overall fracture performance of the in situ composites was relatively poor compared with PC/PBT. Experimental results were compared with those predicted in composite theory. Simplified micromechanics equations were developed to describe the tensile moduli of injection molded LCP reinforced blends that exhibited a strong skin-core morphology.     

A gradient structure formed in injection‐molded polycarbonate in situ hybrid composites and its corresponding performances

Three polycarbonate (PC) composites that were reinforced, respectively, with liquid crystalline polymer (LCP), glass fibers, and both of them were prepared by a single injection‐molding process. The role of LCP in improving the processibility of the composites was characterized by torque measurement test. The transitions of LCP morphology in two‐ and three‐component composites were investigated by using polarizing optical microscopy and scanning electron microscopy. The micrographs showed a skin–core gradient structure in all three systems investigated, and the addition of glass fiber to the PC/LCP blend affected the morphological transition and content distribution of dispersed LCP phase through the thickness of the injection‐molded samples. These results were correlated well with the measurements of tensile mechanical properties and dynamic mechanical analysis. How to fully use the dispersed LCP phase in PC in situ hybrid composites was discussed for the thickness change of core layer and the heterogeneous distribution of more LCP in the core. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 625–634, 2004     

Improvement of the Properties of PC/LCP/MWCNT with or without Silane Coupling Agents

Present study concentrates on the effect of silane coupling agent on the properties and dispersibility of multi-walled carbon nanotube (MWCNTs) in the Polycarbonate (PC)/Liquid Crystalline Polymer (LCP) system. Thermal stability of the PC/LCP/MWCNTs has been improved in an appreciable manner with the addition of silane coupling agents, as revealed from thermogravimetric analysis. Storage modulus also enhanced on addition of silane coupling agent into PC/LCP/MWCNTs systems. Field Emission Electron Microscopic study revealed finer morphology and substantial reduction of the LCP domain, indicating better compatibility between PC and LCP in the presence of a silane coupling agent. High Resolution Transmission Electron Microscopic study supports the unform dispersion of MWCNTs throughout the matrix in the presence of a silane coupling agent.     

Thermal conductivity and thermal expansivity of in situ composites of a liquid crystalline polymer and polycarbonate

The thermal conductivity and thermal expansivity of extruded blends of a liquid crystalline polymer (LCP) and polycarbonate (PC) with volume fraction (V_f) of LCP between 0.09 and 0.8 have been measured as functions of draw ratios λ ranging from 1.3 to 15. At V_f < 0.3, the LCP domains are dispersed in a PC matrix and the aspect ratio of the domains increases with increasing λ. At V_f > 0.55, phase inversion has occurred and the LCP becomes the continuous phase. The axial thermal conductivity K_∥ increases while the axial expansivity α_∥ decreases sharply with increasing λ, as a result of the higher aspect ratio of the LCP fibrils and the improved molecular orientation within the fibrils. Since the transverse thermal conductivity and expansivity are little affected by drawing, the blends exhibit strong anisotropy in the thermal conduction and expansion behavior at high λ. At V_f < 0.3, the behavior of K_∥ is reasonably modeled by the Halpin-Tsai equation for short fiber composites. At high draw ratio (λ = 15), all the blends behave like unidirectional continuous fiber composites, so K_∥ and α_∥ follow the rule of mixtures and the Schapery equation, respectively.     

Development and evaluation of surface treatments to enhance the fiber-matrix adhesion in PAN-based carbon fiber/liquid crystal polymer composites. Part I: Coupling agent and amine surface treatments

Several surface treatments, using both commercially available coupling agents and reagents containing multiple amines, were applied to commingled continuous as-received AS4 carbon reinforcing fiber/liquid crystal polymer (LCP) matrix fibers. Unidirectional composites (normally 60 vol% carbon fiber) were prepared from as-received and treated commingled fibers and characterized. To estimate the effect the effect of the treatments on fiber-matrix adhesion, short beam shear (SBS) tests were conducted, the failure surfaces were examined, and spectroscopic studies wee performed. The mean SBS strength of the as-received unidirectional AS4 carbon fiber/LCP matrix composite system was 49 MPa. The best coupling agent and amine treatments yielded increases in composite shear strength of ∼ 10 to 20%, relative to the as-received AS4/LCP system. For the amine treatments, ESCA and FTIR analyses suggested of both the carbon and LCP fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers (both with coupling agents and amines) showed that strong fiber-matrix adhesion was present. That is, failure occurred in the LCP matrix material.     

TP／LCP原位复合材料

综述了以PP、PET、PC等几种常见的热塑性高聚物为基体的LCP(液晶共聚酯)原位复合材料,讨论了TP(热塑性高聚物)/LCP的结构与性能以及TP与LCP之间的相容性。     

Morphological Characteristics and the Modulus of Liquid Crystalline Polymer Fibers Dispersed in a Thermoplastic Matrix

The morphology of a polycarbonate (PC)-based blend containing a thermotropic liquid crystalline polymer (LCP) component has been characterized in terms of the layer structure, layer thickness, aspect ratio, and number of the shear-induced fibers developed during injection molding. This dispersed LCP phase was still embedded as fibers and deformed droplets in the PC matrix, and their tensile modulus was usually unknown due to the testing problems. Based on the morphological characteristics, a calculation procedure has been developed to estimate the modulus of these fibers and droplets by using a set of micromechanical models. It has been found that the average tensile modulus of these shear-induced LCP fibers and deformed droplets seems to be a material constant, independent of the injection molding condition, i.e., the shear flow condition. For the LCP Vectra A950 studied, the calculated tensile modulus was 24.0 GPa. This value was in fair agreement with that reported in literature. It was larger than that of the injection-molded pure LCP samples and smaller than that of the drawn pure LCP strand.     

Mechanical and morphological properties of carbon fiber reinforced–modified epoxy composites

Epoxy, prepared through aminomethyl 3,5,5‐trimethylcyclohexylamine hardening of diglycidylether of bisphenol‐A (DGEBA) prepolymer, toughened with polycarbonate (PC) in different proportions, and reinforced with carbon fiber, was investigated by differential scanning calorimetry, tensile and interlaminar shear strength testing, and scanning electron microscopy (SEM). A single glass transition temperature was found in all compositions of the epoxy/PC blend system. The tensile properties of the blend were found to be better than that of the pure epoxy matrix. They increased with PC content up to 10%, beyond which they decreased. The influence of carbon fiber orientation on the mechanical properties of the composites was studied, where the fiber content was kept constant at 68 wt %. Composites with 45° fiber orientation were found to have very weak mechanical properties, and the mechanical properties of the blend matrix composites were found to be better than those of the pure epoxy matrix composites. The fracture and surface morphologies of the composite samples were characterized by SEM. Good bonding was observed between the fiber and matrix for the blend matrix composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3529–3536, 2006     

Evaluation of fiber surfaces treatment and sizing on the shear and transverse tensile strengths of carbon fiber-reinforced thermoset and thermoplastic matrix composites

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off-axis directions. The materials of interest in this study were PAN-based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short-beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber-reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber-matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, respectively.     

Rheological hybrid effect in dually filled polycarbonate melt containing liquid crystalline polymer

Polycarbonate (PC)/liquid crystalline polymer (LCP) blends dually filled with glass fiber and nano‐SiO₂ were prepared by melt blending, with the use of a commercial Vectra A130 as the source of LCP and glass fiber. In these dually filled PC/LCP melts, rheological hybrid effect occurred, confirmed by the melt viscosity of the quadruple polymer blends decreased with increasing nano‐silica loading, influenced by the minor LCP phase in the blend. The drastic viscosity reduction closely correlates with the deformation and fibrillation of LCP droplets in the system. The LCP fibrillation was controlled jointly by the thermodynamic and hydrodynamic driving forces. Finally, the dually filled PC/LCP melt had decreased viscosity lower than those of pure PC, silica‐filled PC, and PC/Vectra A130 blends, and furthermore had decreased glass fiber breakage, shown by larger average aspect ratio than that in PC/Vectra A130 blends. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Compatibilization by sulfonate ionomers in polyblends with thermotropic liquid crystalline polymers

It is shown by differential scanning calorimetry (DSC) measurements that lightly sulfonated polystyrene (SPS) is partially miscible with polysulfone (PSF), polycarbonate (PC), polyetherimide (PEI), and a thermotropic liquid crystalline polymer (LCP). Fourier transform infrared analysis confirms that the miscibility of SPS and PSF, and of SPS and PC, comes from the ion–dipole interaction between the sulfonate groups of SPS and the polar groups of PSF and PC, respectively. After the addition of SPS to LCP/PSF, LCP/PC, and LCP/PEI blends, this specific interaction leads to the compatibilization of SPS in these blends, which is revealed by inward glass transition temperature shifts of component polymers in DSC and dynamic mechanical analysis thermograms and by a much finer dispersion of the minor LCP phase in these matrix polymers. The utilization of SPS as the compatibilizer results in a stronger interfacial adhesion between LCP and matrix phases and improves the mechanical performances of LCP/PSF, LCP/PC, and LCP/PEI blends as well. Compared with ternary LCP/PSF, LCP/PC, and LCP/PEI blends with polystyrene as an inert third component, the ternary LCP/SPS/PSF, LCP/SPS/PC, and LCP/SPS/PEI blends have significantly enhanced tensile strengths and moduli, with acceptable processabilities at the same time. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2141–2151, 1998     

Studies on a terephthalic acid and dihydroxydiphenyl sulfone liquid crystalline copolymer and its composites with different thermoplastics

A liquid crystalline polymer (LCP) was synthesized by an interfacial polycondensation reaction at room temperature from terephthaloyl chloride and p,p′-dihydroxydiphenyl sulfone. The LCP synthesized was so stable and molecularly rigid that it did not show any phase transition until it degraded at about 320°C. Composites of the LCP with polycarbonate (PC), polystyrene (PS), and sulfonated polystyrene (SPS) were formed by compression molding at a temperature at which the thermoplastic matrix was in the melt state. They were thermally analyzed by differential scanning calorimetry. Tensile specimens were cut from the compression-molded plates, and mechanical tests were performed. The morphology of the material systems was studied by performing scanning electron microscopy analysis on cryogenically fractured specimens. For LCP/PS and LCP/SPS systems, a sharp two-phase morphology was formed, which suggested poor interfacial adhesion. The tensile strength of both systems decreased with LCP addition. The LCP/PC system also revealed a two-phase morphology; however, the interfaces between the LCP domains and the PC matrix were not so well defined, showing better interfacial adhesion than the two previous systems studied. Stronger bonding between the LCP and PC resulted in a significant improvement in the mechanical behavior of PC by LCP addition. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 645–652, 1997     

Physical properties of blends of polycarbonate and a liquid crystalline copolyester

Blends of polycarbonate (PC) and poly(ethylene terephthalate-co-p-oxybenzoate) (PET/PHB60) were prepared by melt-blending. Physical and/or chemical interactions between the two phases of the system were studied by thermal analysis and infrared spectroscopy. Rheological measurements in shear flow were carried out both in the low and high shear rate regions in the temperature range of the existence of the mesophase. At low liquid crystalline polymer (LCP) content, the blends showed flow curves similar to those of the unfilled PC, while at higher LCP percentages the rheological behavior of the pure LCP was resembled. Moreover, in the whole shear range, the viscosity values of such blends were in between those of the pure polymers. The influence of the addition of 10% LCP on the mechanical properties of the PC was investigated. Fiber-spinning was performed under different experimental conditions, and it was found that opportune drawing conditions are necessary to improve the modulus of the matrix. Morphological analyses of the pure LCP and of the blends were related to the rheological and mechanical behavior of these systems. While the LCP exhibited an elevated dimensional stability, the inclusion of the LCP in PC matrix did not improve the dimensional stability of the blends.     

Generation of fibrillar morphology in blends of block copolyetheresteramide and liquid crystal polyester

Polymer blends comprising liquid crystal polymers, LCP, as a minor component can be formed into fibrillar-type morphology. This morphology enables the generation of improved mechanical properties in the draw direction, in a manner comparable to unidirectional composites: In this paper, the results obtained for blends of a polyetheresteramide block copolymer, PEBA, with a liquid crystalline copolyester are presented. Films prepared using a single-screw extruder were melt drawn on calendering rolls. The blends' storage modulus increased with draw ratio, λ, reaching a maximum value for λ = 3–4. The storage modulus of blends containing 30 wt% LCP, and drawn to λ = 4 to 12, was found to increase nearly 50-fold in comparison to neat PEBA (from 18 MPa to almost 1 GPa). The blends' morphology was characterized by dissolving the PEBA matrix, followed by gravimetric and microscopic analysis of the LCP phase. As expected, the average fiber diameter decreased as a function of λ^−0.5. The fiber content as a function of λ followed a trend parallel to that of the modulus. Longitudinal and transverse moduli followed the Halpin-Tsai predictions for unidirectional composites. Properties of compression molded specimens prepared from these blends compared favorably with glass fiber composites.     

The effect of composition on thermal,mechanical, and morphological properties of thermotropic liquid crystalline polyester with alkyl side-group and polycarbonate blends

A thermotropic liquid crystalline polymer (LCP) with an alkyl side-group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases.     

Transesterification-controlled compatibility and microfibrillation in PC-ABS composites reinforced by phosphorus-containing thermotropic liquid crystalline polyester

For polymer/liquid crystal polymer (LCP) blend systems, the in-situ fibrillation of LCP in polymer matrix can result in the self-reinforcement of polymer/LCP composites. How to control the microfibrillation of LCP in matrix is a key to enhance the mechanical properties of composites. In this paper, we investigated the transesterification-controlled compatibility and microfibrillation of phosphorus-containing thermotropic liquid crystalline polyester, poly(p-hydroxybenzoate-co-DOPO-hydroquinone ethylene terephthalate) (PHBDET) in the PC/acrylonitrile-butadiene-styrene copolymer blend (PC-ABS) during the melt processing. A standard mode and temperature-modulated differential scanning calorimetry (DSC and TMDSC) and ¹³C nuclear magnetic resonance (¹³C NMR) were used to investigate the transesterification and compatibility of PHBDET with PC-ABS. Microstructures, rheological and mechanical properties of the composites were also studied via scanning electron microscopy (SEM), dynamic rheological measurement and universal material testing machine. The results showed that the extent of transesterification could influence the compatibility of PHBDET with PC-ABS, and could be controlled by processing temperature and time. The improved compatibility was not always favorable for the microfibrillation of PHBDET in PC-ABS, but a certain extent of transesterification showed a positive influence on the tensile properties of the composites. Therefore, there existed an optimal extent of transesterification, in which the composite could show a good balance of compatibility and tensile properties.