Addition Of Liquid Crystalline Polymer Research Articles

Investigation into the morphology, crystallization and melting behaviour of nylon 6,6/LCP blends

The morphology, isothermal crystallization and melting behaviour of melt-mixed nylon 6,6/Vectra A950 liquid crystalline polymer (LCP) blends were investigated. The blends formed an immiscible system for all compositions, and the inclusion of LCP, especially at low content, accelerated the bulk crystallization rate of the matrix. The addition of LCP was also found to decrease the crystallite size in the growth direction. The effect of thermal history on the triple melting behaviour and the equilibrium melting temperature was discussed. The equilibrium meting temperature was determined to be lower in the blends. Lauritzen-Hoffman analysis on the crystallization data revealed an apparent regime I to II transition in all the samples. The blends showed lower fold surface energy and work of chain folding as compared to nylon 6,6.

Nonisothermal crystallization kinetics of nylon 66/LCP blends

The non isothermal crystallization kinetics and melting behaviour of nylon 66/thermotropic liquid crystalline polymer (LCP) blends was investigated using differential scanning calorimetry (DSC). In the blends, LCP, at low concentrations, accelerated the bulk crystallization rates of the matrix. However, at high concentrations, it posed a hindrance to the crystallization process. The Avrami, modified Avrami, Ozawa and Mo models were used to fit the experimental data. The effective energy barrier was estimated using Friedman method. The inclusion of LCP had led to lowered energy barrier to crystallization and increased nucleation activity. Moreover, application of Lauritzen Hoffman surface nucleation theory revealed that the addition of LCP, in low concentrations, reduced the work of chain folding and increased the regime I to II transition temperature.

Morphology, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer blends

The miscibility, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer (LCP) blends were studied using differential scanning calorimetry. The blends were found to form primarily an immiscible system. The addition of LCP accelerated the overall rate of crystallization and caused a depression in equilibrium melting temperature, especially at low LCP content. Lauritzen–Hoffman analysis showed that the addition of LCP caused a reduction in the fold surface energy and increased the regime II to III transition temperature.

Studies on the engineering properties of LCP-Vectra B 950/PP blends with the variations of EAA content

Polypropylene (PP) was melt blended with Vectra B-950 [a thermotropic liquid crystalline polymer (LCP)], in a single screw extruder in presence of different doses of ethylene acrylic acid (EAA) copolymer, as modifier. The effect of incorporation in different proportions of EAA at a fixed dose of 5% LCP, on mechanical, thermal, morphological, and rheological properties of such blends was studied and the same were compared with that of pure PP and amongst themselves. Mechanical analysis (tensile properties) of the prepared blends exhibited improvements in ultimate tensile strength (UTS), modulus, toughness, hardness, and impact strength of PP matrix with the incorporation of EAA. The improvement in mechanical properties is associated with the formation of LCP fibrils as evidenced by scanning electron microscopy (SEM). A strong interaction through H-bonding between the segments of Vectra B-950 and EAA was established by FTIR study. Differential scanning calorimetry (DSC) studies indicated substantial increase in melting point of the blends, and thermogravimetric analysis (TGA) showed that the thermal stability of PP was improved with the addition of LCP and EAA. Rheological properties showed that LCP and EAA drop down the melt viscosity of PP and thus facilitate processibility of blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Phase Behavior and Thermal Properties of Polypropylene In Situ Reinforced with Liquid Crystalline Polymer and rPET

In this study, the potential of recycled polyethylene terepthalate (rPET) as a well-defined reinforcing material for the in situ microfibrillar reinforced composite was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with polypropylene (PP) by using an extrusion process. The rheological behavior, morphology, and thermal stability of LCP/PP and rPET/PP blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of LCP or rPET into PP significantly improved the processability. Especially for the blends with 20 and 30 wt% rPET, the potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of the rPET/PP system was lower than that of the LCP/PP system, most rPET domains appeared as small droplets. An addition of LCP and rPET into PP matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and thermally stable reinforcing material similar to LCP.

Effect of LCP and rPET as reinforcing materials on rheology, morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

AbstractMicrofibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Influence of liquid crystalline polymer and recycled PET as minor blending components on rheological behavior, morphology, and thermal properties of thermoplastic blends

AbstractIn this study, the potential of recycled poly(ethylene terepthalate) (rPET) as a well‐defined reinforcing material for the in situ microfibrillar‐reinforced composite (iMFC) was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with high density polyethylene (PE) by using extrusion process. The rheological behavior, morphology, and the thermal stability of LCP/PE and rPET/PE blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of LCP or rPET into PE significantly improved the processability. A potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as‐extruded strand. Although the viscosity ratio of the rPET/PE system was lower than that of the LCP/PE blend system, most rPET domains appeared as small droplets. An addition of LCP and rPET into the PE matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and good thermally resistant material similar to LCP. Copyright © 2009 John Wiley & Sons, Ltd.

Comparative study on phase and properties between rPET/PS and LCP/PS in situ microfibrillar-reinforced composites

Microfibrillar-reinforced composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate) (rPET), and polystyrene (PS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of LCP/PS and rPET/PS blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into PS significantly improved the processability. The potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of rPET/PS system was lower than that of LCP/PS system, most rPET domains appeared as small droplets. An addition of LCP and rPET into PS matrix improved the thermal resistance in air significantly. The obtained results suggested the high potential of rPET as a processing aid and thermally stable reinforcing-material similar to LCP. The mechanical properties of the LCP-containing blends were mostly higher than those of the corresponding rPET-containing blends when compared at the same blend composition.

Viscoelastic properties of in situ composite based on ethylene acrylic elastomer (AEM) and liquid crystalline polymer (LCP) blend

Viscoelastic properties of in situ ethylene acrylic elastomer composites containing 10 and 20 wt.% of liquid crystalline polymer (LCP) were measured in dynamic mechanical experiments. The results show the significant improvement in the storage modulus of the composites with increasing LCP content. All the composites exhibits a single relaxation, which is glass to rubber transition, observed as a peak in the loss modulus at 1 Hz. The time–temperature superposition principle was applied for the pure ethylene acrylic elastomer (AEM) and its composites, in order to evaluate the changes in the viscoelastic properties of AEM by the addition of LCP. Temperature dependence of the shift factors were described using both the Arrhenius and William–Landel–Ferry (WLF) model at the glass transition region. The activation energies of the shift factors are increases with increasing temperature due to complexicity in the motions of the polymer chains, which is further confirmed by the large activation entropies. The principle of time–temperature superposition is used to study changes in the relaxation spectra of in situ AEM system. It is suggested that the change in the viscoelastic behavior, in the case of LCP reinforced AEM, is due to altered molecular mobility of the polymer chain segments in the vicinity of the LCP phase.

Binary Blends of Polytetrafluoroethylene and Liquid Crystalline Polymer

Blends of polytetrafluoroethylene (PTFE) and liquid crystalline polymer (LCP) were prepared by varying the amount of LCP when using a melt mixing technique. The rheological, morphological, thermal, and dynamic mechanical properties of the blends were investigated. The viscosity of the blends was decreased with the increasing LCP content in the blends up to 20% of LCP. With further loadings of LCP a slight improvement in viscosity was observed. This decrease in the viscosity was attributed to be the interlayer slip of the polymers due to formation of the elongated fibrils of LCP, whereas at higher amounts of LCP the fibril nature of LCP was not apparent, which is revealed by the scanning electron microscopic study. The differential scanning calorimetry (DSC) results showed a shift in the melting temperature (Tm) of PTFE with the addition of LCP. This shift in the Tm of PTFE is due to increasing crystallinity. This is further supported by the X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) studies.

A Study of Rodrun LC3000/PP Blends Under Different Stationary and Non-Stationary Shear Conditions: The Influence of LCP Content and Processing Temperature

Blends containing liquid crystalline polymers and thermoplastics have been a topic of great interest for the scientific community due to their excellent performance and properties and thus, promising use in industrial applications. For that reason, from the eighties until today, these systems were widely studied and characterized in terms of their mechanical, morphological, and rheological properties under stationary conditions but not under non-stationary ones which are, in fact, those most relevant to processing sequences. Thus, despite all the published work on this subject, there is still a need to study the response of the materials under the latter conditions. The transient shear measurements performed on the blends of Rodrun LC3000 and PP showed an overshoot for the transient stress, the magnitude of which increases with increasing LCP content. This overshoot is attributed to the orientation and deformation of the LCP structures. The results obtained for the blends by Large Amplitude Oscillatory Shear, LAOS, were revealed to be highly sensitive (compared with those observed in steady shear measurements) not only to the LCP content, but also to the processing temperature. From the rheological point of view an unusual behavior was observed for these systems, which was characterized by an increase of the viscosity and storage modulus with the increase of the LCP content at low frequencies, but a decrease at high frequencies. The traditional and well-known decrease of steady shear viscosity and mechanical improvement, induced by the addition of liquid crystalline polymer to the thermoplastic, was also observed.

Self-Reinforcing Composite Based on Ethylene Acrylic Elastomer (AEM)/Liquid Crystalline Polymer (LCP) Blend

Blends of ethylene acrylic elastomer (AEM) and thermotropic liquid crystalline polymer (TLCP) have been prepared by melt mixing technique. Processing studies indicated a decrease in the viscosity of the blends with the addition of liquid crystalline polymer (LCP). At lower level of LCP the tensile strength and tear strength increased. However, at higher level of LCP tensile strength values decreased due to insufficient adhesion between two phases. The modulus of the samples increased with the LCP content. The degree of crystallinity increased with increasing LCP content. This improvement in crystallinity is associated with the increase in crystallite size. For the blends, thermal studies indicated, the endothermic signals which were more prominent at all the peak temperatures. The heat of degradation values increased with the LCP content. Scanning electron microscope (SEM) study suggested the fibril formation, which affected the failure mechanism under DMA studies. Storage modulus and loss modulus of the blends increased with increasing LCP content. At above glass transition temperature (Tg) improvement in storage modulus is nearly five times higher than that of the pure AEM.

Blends of silicone rubber and liquid crystalline polymer

Blends of silicone rubber(VMQ) and liquid crystalline polymer(LCP) were prepared by the melt mixing technique. Mechanical, XRD, thermal and dynamic mechanical investigations are reported for the pure silicone rubber and blends. The mechanical properties, viz. the tensile strength, tear strength and elongation at break, of the silicone rubber decreased with the addition of LCP. The SEM study on the tensile fractured surface of the blends revealed that they had a two phase structure, and that the failure was mainly due to fiber pull out, which suggests that the VMQ and LCP are incompatible in all of the proportions examined in this study. However, the FTIR study shows that there was a partial interaction between the VMQ and LCP, but which may not be sufficient to grip the fibrils under the applied load. In the XRD analysis, it was observed that the crystalline structure of the silicone rubber deteriorated in the presence of LCP. The DMA study suggested that the storage modulus of the silicone rubber was improved with the addition of LCP, due to the high modulus of the LCP phase. The thermal stability of the silicone rubber was greatly reduced by the addition of LCP, due to the latter having a thermal stability lower than that of silicone rubber.

Viscoelastic properties of ternary in situ elastomer composites based on fluorocarbon, acrylic elastomers and thermotropic liquid crystalline polymer blends

Dynamic mechanical analysis was performed to characterize the viscoelastic properties of binary and ternary blends of fluorocarbon elastomer (FKM), acrylic elastomer (ACM) and liquid crystalline polymer (LCP). The results showed that the storage and loss modulus of all the blends increased significantly with the weight percentage of the LCP. The glass transition temperature evaluated at the loss modulus peak, were in the range of −10–+5 °C for all the blends. The time temperature superposition principle was applied for the FKM/ACM and 20% LCP filled FKM/ACM blend in order to evaluate the changes in the viscoelastic properties of FKM/ACM blend by the addition of LCP. The Arrhenius and William–Landel–Ferry (WLF) equations were used to quantify the viscoelastic behaviour at the glass transition region. Both the blends exhibited a single relaxation, which is glass transition, observed as a peek in the loss modulus at 1 Hz. The glassy moduli of these two systems were found to be comparable, but the rubbery moduli of the LCP filled FKM/ACM was much higher than the LCP unfilled system. However, the viscoelastic behaviour of these two systems and their sensitivity to time temperature may be considered to be quite similar.

In-situ elastomer composite based on fluorocarbon elastomer/liquid crystalline polymer blend

Blends of fluorocarbon elastomer (FKM) and liquid crystalline polymer (LCP) have been prepared by melt mixing technique. Processing studies indicated the decrease in the viscosity and the state of cure with the addition of 10 wt% LCP, and then increased at a higher rate with the addition of more LCP to the blend. The tensile strength values decreased at lower level of LCP. However, the modulus and tear strength values increased with higher increment of LCP content. From the X-ray diffraction measurements it has been observed that the crystalline structure of the FKM is greatly affected by the addition of LCP. The degradation temperatures from thermogravimetric analysis (TGA) suggested improved thermal stability of the fluorocarbon-LCP blends. From the dynamic mechanical analysis (DMA), it has been found that the glass transition temperature (T g) of the blends increased with increase in LCP content. For the compositions of 10 wt% and 20 wt% LCP blends, enhancement in storage modulus is found above the glass transition of FKM. Under dynamic conditions the increase of LCP content restricts the matrix flow and hence cracks developed at the interface of the LCP fibrils and matrix.

Mechanical, dynamic mechanical properties and thermal stability of fluorocarbon elastomer-liquid crystalline polymer blends

Blends of fluorocarbon elastomer (FKM) and liquid crystalline polymer (LCP) have been prepared by the melt mixing technique. Processing studies indicated the increase in viscosity with the addition of LCP. The tensile strength, tear strength, and modulus of the elastomer are greatly improved by the addition of the LCP. Dynamic mechanical analysis (DMA) results showed that the shift in the glass transition temperature (Tg) of the elastomer with the addition of LCP and the storage modulus of the blends increased above the Tg of FKM, whereas decreases below the Tg of the elastomer were seen with up to 20 wt% LCP; this suggests that the LCP acts as an effective reinforcing agent above the Tg of FKM. From the thermogravimetric analysis (TGA) and differential thermogravimetry (DTG), we found that the thermal stability of the elastomer enhances by blending with the LCP. The weight loss and the weight loss rate of the FKM decrease enormously with the addition of LCP. From the X-ray diffraction (XRD) study, it has been observed that the LCP acts as a nucleating agent by increasing the crystallinity of the blend. The failure mechanism of the blends was studied using a scanning electron microscope (SEM). It suggested that the failure occurred in the blends; mainly due to the pull out of the fibrils from the matrix phase and due to lower interfacial adhesion between the LCP phase and the elastomer. POLYM. COMPOS. 26:306–315, 2005. © 2005 Society of Plastics Engineers

Self‐reinforcing elastomer composites based on ethylene–propylene–diene monomer rubber and liquid‐crystalline polymer

AbstractIn this study, the prime factor determining the size, shape, and distribution of liquid‐crystalline polymer (LCP) was the viscosity ratio at the processing conditions. The fiber‐forming capacity of the LCP depended on the viscosity of the ethylene–propylene–diene monomer rubber (EPDM). With increasing LCP content, the tensile and tear strengths did not increase, perhaps because of incompatibility between the EPDM and LCP. The hardness increased because of the hard mesogenic groups in the LCP. The percentage swelling decreased as the LCP content increased. With increasing LCP content, processability became easier because of a lower melt viscosity. The scorch time increased at higher LCP levels. A higher percentage crystallinity was observed with increasing LCP content. Scanning electron microscopy clearly showed the fiber phase formation, which was two‐dimensionally isotropic in nature, confirming fiber formation even in a shear field. The addition of LCP improved the thermal stability. The onset degradation temperatures shifted to higher values with increasing LCP content. Dynamic mechanical thermal analysis revealed that with the addition of LCP, the mechanical damping increased at its lower level. High‐temperature processing increased the effective amorphous zone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 711–718, 2004

Properties of radiation-modified blends of polyethylene with elastomers and liquid crystalline copolyester

The results are given on the effect of γ-irradiation on properties of blends of high and low-density polyethylene (HDPE, LDPE) with elastomers -ethylene/propylene/diene rubber (EPDM) and chlorinated polyethylene (CPE), and thermotropic liquid crystalline polymer (LCP). The morphological, thermal, mechanical properties (including thermosetting properties) and adhesion properties of blended composites were investigated. A special attention was paid to the applicability of the blends as thermosetting materials (TSM). The LCP used was a copolyester of poly(ethylene terephthalate) with p-(hydroxybenzoic acid) in the ratio 40 : 60. It was found that addition of LCP essentially influenced the thermomechanical and adhesion properties of PE composites, irradiated up to the absorbed dose 150 kGy, as well as the dimensional stability of thermosetting products, made from polyethylene/elastomer mixtures. The results show that such ternary blends considerably improve the exploitation conditions of irradiated polyethylene and useful thermosetting materials can be obtained.

Blends of poly(ethylene 2,6-naphthalate) with liquid-crystalline polymers: crystallization behavior and morphology

The isothermal crystallization behavior and morphology of blends of Poly(ethylene 2,6-naphthalate) (PEN) with two types of liquid-crystalline polymers (LCP) (rigid and semiflexible) have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The blends posses a two-phase morphology due to immiscibility of the two components. The dispersion of the minor LCP phase is favored at a low LCP concentration (7wt%). The PEN overall crystallization rate is enhanced strongly by the addition of LCPs. The maximum enhancing effect has been found to occur at a LCP concentration of ca. 7wt%. The POM observations show that PEN spherulite dimensions decrease in the presence of LCPs. These results have been interpreted on the basis of a heterogeneous nucleation played by the crystallized LCP particles on the molten PEN matrix. The nucleation mechanism and the equilibrium melting temperature of PEN are not changed by the presence of a dispersed LCP phase. The relationship between blend morphology and nucleation phenomena has been discussed.

The effect of a third component on the morphology and mechanical properties of liquid-crystalline polymer and polypropylene in situ composites

Maleic-anhydride-grafted PP (MAGPP) and polycarbonate (PC) were used as the third component and their effect on the morphology and the mechanical properties of in situ composites of Rodrun liquid-crystalline polymer (LCP) and polypropylene (PP) has been investigated. The addition of LCP in a PP matrix resulted in an increase in tensile modulus but a decrease in tensile strength. The addition of MAGPP as third component in the LCP/PP binary system has considerable effect on both the tensile strength and tensile strain. Furthermore, the introduction of PC in the LCP/PP binary system resulted in a significant increase in tensile modulus, tensile strength and tensile strain. The 30 wt% of PC in the LCP/PP/PC ternary system was an optimum value for the best mechanical properties. A lamella-like morphology was found at the tensile fracture surface of the LCP/PP/PC ternary system whereas it was ribbon-like structure in the LCP/PP binary system.