Study on in situ reinforcing and toughening of a semiflexible thermotropic copolyesteramide in PBT/PA66 blends

Ternary in situ composites based on poly(butylene terephthalate) (PBT), polyamide 66 (PA66), and semixflexible liquid crystalline polymer (LCP) were systematically investigated. The LCP used was an ABA30/PET liquid crystalline copolyesteramide based on 30 mol % of p‐aminobenzoic acid (ABA) and 70 mol % of poly(ethylene terephthalate) (PET). The specimens for thermal and rheological measurements were prepared by batch mixing, while samples for mechanical tests were prepared by injection molding. The results showed that the melting temperatures of the PBT and PA66 phases tend to decrease with increasing LCP addition. They also shifted toward each other due to the compatibilization of the LCP. The torque measurements showed that the ternary blends exhibited an apparent maximum near 2.5–5 wt % LCP. Thereafter, the viscosity of the blends decreased dramatically at higher LCP concentrations. Furthermore, the torque curves versus the PA66 composition showed that the binary PBT/PA66 blends can be classified as negative deviation blends (NDBs). The PBT/PA66/LCP blends containing up to 15 wt % LCP were termed as positive deviation blends (PDBs), while the blends with the LCP ≥25 wt % exhibited an NDB behavior. Finally, the tensile tests showed that the stiffness and tensile strength of ternary in situ composites were generally improved with increasing LCP content. The impact strength of ternary composites initially increased by the LCP addition, then deteriorated when the LCP content was higher than 10 wt %. The correlation between the mechanical properties and morphology of the blends is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1975–1988, 2000     

Dynamic rheological properties of polyetherimide/polyetheretherketone/liquid crystalline polymer ternary blends

The dynamic rheological properties of poly(etherimide)/poly(etheretherketone)/liquid crystalline polymer (LCP) ternary blends were measured in order to correlate these properties with the morphology obtained after extrusion. The viscosity radio, η_d/η_m, where η_d = disperse phase viscosity and η_m = matrix viscosity, had to be redefined. Below 50 wt% LCP, η_d = η_LCP, η_m = η_PEEK+PEI and η_d/η_m < 1. Above 50 wt% LCP, η_d = η_PEEK+PEI, η_m = η_LCP and η_d/η_m > 1. Fibrillar morphologies were obtained in both cases, except below a concentration of 20 wt% LCP. At low concentrations of LCP the ternary blends had lower viscosities than the component polymers, showing a flow promotion effect of the LCP on the PEI- and PEEK-rich phases.     

Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites

Liquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (F_max), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.     

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.     

Effect of dispersed phase on the morphology of in situ microfibrils and the viscoelastic properties of its composite via direct extrusion

A triangle arrayed triple‐screw extruder was used to prepare in situ polypropylene (PP) microfibrillar composites (MFCs) by direct extrusion, in which polyamide 6,6 (PA66) and poly(butylene terephthalate) (PBT) were used as dispersed phases while PP as matrix phase. The morphological evolution of the dispersed phase were investigated by SEM through taking samples along the extruder from different positions. The results showed that the fibrillating mechanism of PA66 was entirely different from that of PBT. Dynamic oscillatory shear rheological properties were used to analyze the effect of different types of in situ microfibrils on the rheological properties of MFCs. The obtained results showed that the storage modulus and complex viscosity of both PP/PA66 and PP/PBT MFCs were improved with increasing fibrillar aspect ratios. The loss tangent tan δ at low frequencies decreased with the increase of fibrillar aspect ratio. Moreover, the gel point concentration of PP/PA66 composite was lower than that of PP/PBT composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46286.     

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     

Poly(butylene terephthalate)–clay nanocomposites prepared by melt intercalation: morphology and thermomechanical properties

Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (η_inh), were used for this study (η_inh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry     

Compatibilizing effect of styrene–maleic anhydride copolymer on the properties of polyamide‐6/liquid crystalline copolyester composites

Liquid crystalline polymer–polyamide‐6 (LCP/PA6) composites containing 20 wt % LCP content were compatibilized by a random styrene–maleic anhydride copolymer (RSMA). The blending was performed via extrusion followed by injection molding. The LCP employed was a commercial copolyester, Vectra A950. The dynamic mechanical (DMA), rheological, thermal, and mechanical properties as well as the morphology of the composites were studied. The DMA and rheological results showed that RSMA is an effective compatibilizer for LCP/PA6 blends. The mechanical measurements showed that the stiffness, tensile strength, and toughness of the in situ composites are generally improved with increasing RSMA content. However, these mechanical properties deteriorated considerably when RSMA content was above 10 wt %. The drop‐weight dart impact test was also applied to analyze the toughening behavior of these composites. The results show that the maximum impact force (F_max) and crack‐initiation energy (E_init) tend to increase with increasing RSMA content. From these results, it appeared that RSMA prolongs the crack‐initiation time and increases the energies for crack initiation and impact fracture, thereby leading to toughening of LCP/PA6 in situ composites. Finally, the correlation between the mechanical properties and morphology of the blends is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1964–1974, 2000     

The effect of the viscosity ratio of dispersed phase to matrix on the rheological,morphological, and mechanical properties of polymer blends containing a LCP

The effect of the viscosity ratio of the dispersed LCP phase to the polystyrene/poly(phenylene oxide) (PS/PPO) thermoplastic matrix on the rheological, morphological, and resultant mechanical properties of the LCP blends was investigated. The viscosity of PS/PPO is largely dependent on the blend composition, so that different levels of viscosity ratios of dispersed LCP phase to PS/PPO thermoplastic matrix are obtained by using PS/PPO premixtures of different blend ratios as a thermoplastic matrix. When the viscosity of the LCP dispersed phase is lower than that of the thermoplastic matrix, finely distributed fibril structure of LCP is obtained. Tensile modulus of injection molded specimens show a positive deviation from the additive rule when the viscosity ratio (η_LCP/η_matrix) is smaller than unity. These improvements in tensile modulus are attributed to the formation of finely distributed LCP fibrils. © 1996 John Wiley & Sons, Inc.     

Rheological and thermal properties of blends of modified poly(ethylene terephthalate) with p‐acetoxybenzoic acid and poly(butylene terephthalate)

Blending of thermotropic liquid crystalline polyesters (LCPs) with conventional polymers could result in materials that can be used as an alternative for short fiber‐reinforced thermoplastic composites, because of their low melt viscosity as well as their inherent high stiffness and strength, high use temperature, and excellent chemical resistance and low coefficient of expansion. In most of the blends was used LCP of 40 mol % of poly(ethylene terephthalate) (PET) and 60 mol % of p‐acetoxybenzoic acid (PABA). In this work, blends of several copolyesters having various PABA compositions from 10 to 70 mol % and poly(butylene terephthalate) (PBT) were prepared and their rheological and thermal properties were investigated. For convenience, the copolyesters were designated as PETA‐x, where x is the mol % of PABA. It was found that PET‐60 and PET‐70 copolyesters decreased the melt viscosity of PBT in the blends and those PBT/PETA‐60 and PBT/PETA‐70 blends showed different melt viscosity behaviors with the change in shear rate, while blends of PBT and PET‐x having less than 50 mol % of PABA exhibited totally different rheological behaviors. The blends of PBT with PETA‐50, PETA‐60, and PETA‐70 showed the morphology of multiple layers of fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1797–1806, 1999     

Shear rate dependence of viscosity and first normal stress difference of LCP/PET blends at solid and molten states of LCP

The liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having 20, 40, 60, 80, and 100 wt % of LCP. Morphology of these samples was studied using scanning electron microscopy. The steady state shear viscosity (η), dynamic complex viscosity (η*) and first normal stress difference (N₁) were evaluated and compared at two temperatures: 265°C, at which LCP was in solid state, and 285°C, at which LCP was in molten state. The PET was in molten state at both the temperatures. The shear viscosity of the studied blends displayed its dependence on composition and shear rate. A maxima was observed in viscosity versus composition plot corresponding to 80/20 LCP/PET blend. The N₁ increased with LCP loading in PET and with the increased asymmetry of LCP droplets. The N₁ also varied with the shear stress in two stages; the first stage demonstrated elastic deformation, whereas second stage displayed dominant plastic deformation of LCP droplets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2212–2218, 2007     

Elastic moduli of a liquid crystalline polymer and its in-situ composites

The elastic moduli of a liquid crystalline polyesteramide (LCP) and polycarbonate/LCP in-situ composites with 10 to 80 wt% of LCP have been measured as functions of draw ratio λ from 1 to 15 by an ultrasonic method. For the LCP, the sharp rise of the axial Young's modulus E₃ and the slight decreases of the transverse Young's modulus E₁ and the axial (C₄₄) and transverse (C₆₆) shear modulus with increasing λ result from the alignment of chains along the draw direction. E₁, C₄₄, and C₆₆ follow the lower bounds calculated using the series coupling scheme of the aggregate model. Although E₃ lies close to the lower bound at low λ, it follows the upper bound calculated according to the parallel coupling scheme at λ > 3. The elastic moduli of the composites have similar draw ratio dependences as those of the LCP. The strong increase in E₃ with increasing λ arises from the higher aspect ratio of the LCP domains in the composites and the improved molecular orientation within the domains. The reinforcement effect on the other moduli is much weaker, with E₁ and C₄₄ of the composites only 5 to 30% higher than those of polycarbonate at λ = 15. Since C₆₆ of the LCP decreases to a value below that of polycarbonate at λ > 2, there is a positive reinforcement effect at low λ but a negative effect at high λ.     

Synthesis and properties of reactively compatibilized polyester and polyamide blends

The functionalization of poly(butylene terephthalate) (PBT) has been accomplished in a twin screw extruder by grafting maleic anhydride (MA) using a free radical polymerization technique. The resulting PBT‐g‐MA was successfully used as a compatibilizer for the binary blends of polyester (PBT) and polyamide (PA66). Enhanced mechanical properties were achieved for the blend containing a small amount (as low as 2.5 %) of PBT‐g‐MA compared to the binary blend of unmodified PBT with PA66. Loss and storage moduli for blends containing compatibilizer were higher than those of uncompatibilized blends or their respective polymers. The grafting and compatibilization reactions were confirmed using FTIR and ¹³C NMR spectroscopy. The properties of these blends were studied in detail by varying the amount of compatibilizer, and the improved mechanical behaviour was correlated with the morphology with the help of scanning electron microscopy. Morphology studies also revealed the interfacial interaction in the blend containing grafted PBT. The improvement in the properties of these blends can be attributed to the effective interaction of grafted maleic anhydride groups with the amino group in PA66. The results indicate that PBT‐g‐MA acts as an effective compatibilizer for the immiscible blends of PBT and PA66. © 2000 Society of Chemical Industry     

Rheological,thermal, and mechanical properties of phosphorus‐containing wholly aromatic thermotropic liquid crystalline polymer‐filled poly(butylene terephthalate) composites

Phosphorus‐containing wholly aromatic thermotropic liquid crystalline polymer (TLCP) reinforced poly(butylene terephthalate) (PBT) composites were prepared. Dynamic rheological analysis displayed that the addition of TLCP led to the decrease of the complex viscosity of PBT. While the thermal stability and tensile modulus were found to be increased distinctly, the results of dynamic mechanical analysis, isothermal crystallization, and morphological observation indicated that these changes were related to the rigid chains and in situ fibrillation of TLCP phase, and the interfacial adhesion between PBT and TLCP. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

A single-mode rheological model for steady flows of polymer melts

The steady shear viscosity (η_s), the steady first normal stress coefficient (Ψ₁), the steady second normal stress coefficient (Ψ₂), and extensional viscosity (η_e) are four important parameters for polymer melts during polymer processing. In this article, we propose a stress and rate-dependent function to describe creation and destruction of polymer junctions. Moreover, we also introduce a movement expression to describe nonaffine movement of network junctions. Based on network theory, a nonaffine single-mode rheological model is presented for the steady flow of polymeric melts, and the equations of η_s, Ψ₁, Ψ₂, and η_e are derived from the model accordingly. Furthermore the dependences of η_s and η_e on model parameters are discussed for the model. Without a complex statistical simulation, the single-mode model with four parameters yields good quantitative predictions of the steady shear and extensional flows for two low density polyethylene melts reported from previous literature in very wide range of deformation rates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt shear viscosity of PP/Al(OH)3/Mg(OH)2 flame retardant composites at high extrusion rates

The melt apparent shear viscosity (η_a) of polypropylene (PP) composites filled with aluminum hydroxide [Al(OH)₃] and magnesium hydroxide [Mg(OH)₂] was measured by means of a capillary rheometer under experimental conditions of temperature ranging from 180 to 200°C and apparent shear rate varying from 10 to 2 × 10³ s⁻¹, to identify the effects of the filler particle content and size on the melt viscosity. The results showed that the melt shear flow of the composites obeyed the power law and presented pseudoplastic behavior. The dependence of η_a on temperature was consistent with the Arrhenius equation. The sensitivity of η_a for the composite melts to temperature was greater than that of the unfilled PP, and weakened with increasing apparent shear rate. The η_a increased linearly with an increase of the weigh fraction of the flame retardant, especially in the low apparent shear rate region. The η_a of the composites decreased slightly with an increase of particle size of flame retardant. Moreover, the variation for the η_a with particle size of flame retardant was much less than with apparent shear rate under these test conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of the molecular structure of impact modifier and compatibilizer on the toughening of PBT/SBS/PS‐GMA blends

This work aims at studying the toughening process of poly(butylene terephthalate) (PBT) through its blends with styrene‐butadiene‐styrene block copolymers (SBS), in the presence of poly(styrene‐ran‐glicydil methacrylate) (PS‐GMA) as reactive compatibilizer. High values of impact strength were attained for PBT/SBS blends without the compatibilizer; however, this improvement is achieved for blends with SBS having similar viscosity compared to PBT, at high SBS content (40 wt %) and for blends prepared under specific processing conditions. The efficiency of the in situ compatibilization of PBT/SBS blends by PS‐GMA was found to be strongly dependent on the SBS and PS‐GMA molecular characteristics. Better compatibilizing results were observed through fine phase morphologies and lower ductile to brittle transition temperatures (DBTT) as the interfacial interaction and stability of the in situ formed compatibilizer are maximized, that is, when the miscibility between SBS and PS‐GMA and reaction degree between PBT and PS‐GMA are maximized. For the PBT/SBS/PS‐GMA blends under study, this was found when it is used the SBS with higher polystyrene content (38 wt %) and with longer PS blocks (M_w = 20,000 g mol^?1) and also the PS‐GMA with moderate GMA contents (4 wt %) and with molecular weight similar to the critical one for PS entanglements (M_c = 35,000 g mol^?1). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5795–5807, 2006     

Rheology and processability of polyamide66 filled with different‐sized and size‐distributed calcium carbonate

Two‐sized calcium carbonates (CaCO₃) were blended and filled into polyamide66 (PA66). The shear viscosity of PA66/CaCO₃ composites was measured with a capillary extrusion rheometer. The results showed that the shear viscosity of the efficient size distribution samples (PA66 was filled with 600/2500 mesh CaCO₃ blending) obviously decreased compared with that of the single‐size distribution samples (PA66 was filled with 600 or 2500 mesh CaCO₃). The shear viscosity of PA66/CaCO₃ composites at different temperatures was also studied. The results showed that the flow activation energy and flow activation entropy of the efficient size distribution samples obviously increased compared with those of the single‐size distribution samples. The change in flow activation entropy was used to explain the experimental results of shear viscosity. The processability of PA66/CaCO₃ composites was evaluated with a HAAKE torque rheometer. The results showed that the processability of the efficient size distribution samples was obviously improved and the best efficiency of processability improvement appeared in the 30 wt% CaCO₃ content. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Morphological structure and mechanical properties of In situ microfibrillar composites of modified PA66 with PP

In situ microfibrillar composites (PP/mPA66) of modified polyamide66 (mPA66) with polypropylene (PP) were prepared by using a “post‐compatibilization” technique. The mPA66 was firstly obtained by reactive extrusion of PA66 resin with a specially designed compatibilizer, which was then blended with PP through extrusion combined with a hot stretching and subsequently quenching process. The PP/mPA66 in situ microfibrillar composites were comparatively studied with simply blended samples of PP/PA66 that were prepared by blending PA66 and PP together with (or without) the same compatibilizer through extrusion. PA66‐g‐PP (and/or elastomers) graft copolymer formation in mPA66 was identified by dissolution test and infrared spectroscopy measurement, the compatibilizer is unevenly dispersed with large domains in PA66 as observed by scanning electron microscope (SEM). In PP/mPA66 composites, the in situ generated PA66 microfibrils have a rather nonuniform diameter distribution and a very rough surface. SEM observations for the fractured surface illustrated that PP/mPA66 composites have structural characteristics of stronger adhesion and moderate flexibility of the interface. Enhanced compatibilization between the PA66 microfibrils with the PP matrix resulted in improved mechanical properties of the PP/mPA66 composites. With optimized composition, the PP/mPA66 composite has notched Izod impact strength, flexural modulus, and tensile yield stress of 1.49, 1.16, and 0.99 times as those of the neat PP, respectively. Such enhanced mechanical properties balance and improved interface adhesion were not found in the simply blended samples of PP/PA66 with or without the specially designed compatibilizer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of viscosity ratio and processing conditions on the morphology of blends of liquid crystalline polymer and polypropylene

The effect of viscosity ratio and processing conditions on LCP/PP blend morphology was studied. The viscosity ratio (η_LCP/η_PP) was varied from 0.1 to 3.6 by using five different polypropylene grades as the matrix and two LCPs as the dispersed phase (20 wt %). The most spontaneous fiber formation was achieved when the viscosity ratio was between 0.5 and 1. In addition to shear forces, elongational forces are important in achieving a highly fibrillar structure and significant mechanical reinforcement. The lubricating effect induced by the low viscosity of LCP was most pronounced for the blends exhibiting a fibrillar morphology. The morphologies of blends produced by different mixing equipment differed only slightly. The greatest variation in the mixing efficiency was found for blends whose components had totally dissimilar melt viscosities. The slight differences in morphology due to melt blending in dissimilar equipment were decreased after injection molding, whereas the differences in morphology due to dissimilar viscosity ratios were still evident in the injection molded blends. Thus, the viscosity ratio at processing in the actual processing conditions is of great importance. © 1994 John Wiley & Sons, Inc.