Yongsok Seo

Study of the crystallization behaviors of polypropylene and maleic anhydride grafted polypropylene

Abstract The crystallization kinetics of isotactic polypropylene (iPP) and maleic anhydride grafted polypropylene (MA–PP) and their blends, crystallized both nonisothermally and isothermally, were investigated by differential scanning calorimetry. During isothermal crystallization, relative crystallinity developed with the time dependence described by the Avrami equation with exponents n ≈2.7 for neat iPP and n ≈3.8 for MA–PP. The half crystallization time for MA–PP was much smaller than that for iPP. The half crystallization time of iPP depended more strongly on the crystallization temperature than that of MA–PP did. A kinetic equation for nonisothermal crystallization was employed to analyze the crystallization characteristics of iPP and MA–PP. The nonisothermal crystallization kinetic analysis for MA–PP at different cooling rates was possible, assuming that the spherulitic growth was initiated by heterogeneous nucleation alone while that for iPP at high cooling rates was successfully done by assuming both homogeneous and heterogeneous nucleations. The diffusional activation energy was smaller for MA–PP than for iPP. The number of heterogeneous nuclei for MA–PP was larger than that for iPP. The presence of MA–PP in iPP affects the crystallization of iPP by acting as a nucleating agent.

Characterization and processing of blends of poly(ether imide) with thermotropic liquid crystalline polymer

Abstract We investigated thermal, rheological, morphological and mechanical properties of an in situ composite of poly(ether imide) (PEI) and thermotropic liquid crystalline polymer (TLCP). Ultem 1000 was used as a matrix and Vectra B950 was used as the in situ reinforcing TLCP. Fibre-spinning of the blends was performed on a capillary rheometer. Differential scanning calorimetry thermograms of extruded fibres indicated that the thermal properties of PEI did not change noticeably with the amount of TLCP but thermogravimetric analysis showed that thermal stability of the blend was decreased with the amount of TLCP. Immiscibility was checked with thermal data. The rheological properties of the blends changed remarkably with temperature and composition. The tensile strength and modulus of blend fibre increased with TLCP content and spin draw ratio. The increase of tensile strength was more striking for the fibre of the blend containing more TLCP. Wide angle X-ray patterns suggested that the increase in tensile strength was due to the enhanced molecular orientation and resultant fibrillation of TLCP. A modified Tsai-Halpin equation was used to predict the aspect ratio of microfibrils for these blends. Morphology of the blend showed that PEI/TLCP fibres contained fine fibrils of almost infinite aspect ratio and nearly perfect orientation in the flow direction. The draw ratio effect on the mechanical properties was remarkable at low draw ratio, but levelled off soon. The amount of TLCP influenced the fibril formation. Morphological observation showed the effect of thermal history of the blend and its effect on mechanical performance. The blend showed maximum aspect ratio and aspect ratio change when TLCP content was 25 wt%. TLCP orientation and its steric effect seem to induce the optimum TLCP amount for fibril formation.

Compatibilizing effect of a poly(ester imide) on the properties of the blends of poly(ether imide) and a thermotropic liquid crystalline polymer: 2. Morphology and mechanical properties of the in situ composite system

Abstract Blends of a thermotropic liquid crystalline polymer (TLCP), [poly(ester amide), PEA, Vectra B950 from Hoechst Celanese] and poly(ether imide) (PEI, Ultem 1000 from G.E.) with the compatibilizer [poly(ester imide), PEsI] were extruded in a twin-screw extruder. The extruded strands were evaluated in terms of morphology and mechanical properties. The morphology of the compatibilized in situ composites was found to be significantly dependent on the concentration of the compatibilizer in the blend. For a TLCP phase content of 25 phr, a maximum reduction in phase size was observed when 1.5 phr by weight of compatibilizer was added to the blend. At high concentrations of the compatibilizer, flocculation of the TLCP phase was observed. Measurement of the tensile properties shows increased elongation as well as enhanced modulus and strength when properly compatibilized. This improvement is ascribed to better adhesion between the TLCP fibrils and the PEI matrix and better dispersion of the TLCP fibrils. Synthesized PEsI significantly improved the adhesion between the matrix phase (PEI) and fibril phase (PEA). However, maxima in tensile modulus, tensile strength and elongation were observed when excess compatibilizer was added. An emulsifying effect of the compatibilizer to coalesce the fibrils is believed to be the cause of the maxima in the tensile properties. Impact strength was seriously increased with the compatibilizer. A maximum in impact strength was also observed, but all compatibilized samples exhibited a higher impact strength than the non-compatibilized one. The reason is believed to be the failure mode difference between the tensile properties and the impact strength.

Compatibilizing effect of a poly(ester imide) on the properties of the blends of poly(ether imide) and a thermotropic liquid crystalline polymer: 1. Compatibilizer synthesis and thermal and rheological properties of the in situ composite system

Abstract This study investigates the compatibilizing effect of a poly(ester imide) (PEsI) on the blends of poly(ether imide)(PEI, Ultem 1000 from G.E.) and thermotropic liquid crystalline polymer (TLCP)(poly(ester amide), PEA, Vectra B950 from Hoechst Celanese). The compatibilizer, PEsI, was synthesized. Composite fibres were prepared by extrusion. Compatibility, thermal and theological properties of the compatibilized in situ composite have been analysed. PEI and PEA blends are known from previous studies to be immiscible. Differential scanning calorimetry (d.s.c.) and dynamic mechanical thermal analysis (d.m.t.a.) results, however, show that PEsI is miscible with both PEI and PEA. This means that synthesized PEsI can be used as a compatibilizer for the PEI/PEA in situ composite system. The viscosity of the compatibilized in situ composite was increased by the compatibilizer owing to the strong interaction. Significant changes in the dispersion of the TLCP were observed when the compatibilizing agent was added. The size of the dispersed phase appears to be controlled by interfacial phenomena rather than rheological effects. Explanations for the interaction of PEsI with PEI and TLCP related to the interfacial phenomena are presented.

Interfacial adhesion and deformation of thermotropic liquid crystal polymers in engineering thermoplastics : Blends of a poly(ester amide) with Nylon 6 and a polyester with PBT

A new method was sought to produce in situ composites by the addition of a third component that would react with matrix polymers and thermotropic liquid crystal polymers to form graft copolymers, which act as a compatibilizer at the interface. Morphological observation reveals the significance of compatibilization in immiscible polymer blends. Good adhesion at the interface by the produced compatibilizer enabled the finely dispersed liquid crystal phase to be deformed in shear flow without elongation, even when the viscosity of the matrix polymer was lower than that of the liquid crystal polymer. This study provides a way to produce a strong and tough in situ composite.

Morphology and properties of compatibilized ternary blends (nylon 6/a thermotropic liquid crystalline polymer/a functionalized polypropylene) processed under different conditions

Abstract Relationships between the properties of ternary blends of nylon 6, a thermotropic liquid crystalline polymer (TLCP, poly(ester amide), 20xa0wt%) and a compatibilizer (maleic-anhydride-grafted polypropylene, MA-PP, 2xa0wt%) are studied under various processing conditions. The immiscible binary blend can be compatibilized by the addition of MA-PP. The compatibilizer provides extrudate surface stability, thus enabling high drawing. Strong elongational flow favors fibril development, which was not possible when maleic-anhydride-grafted ethylene-propylene-diene terpolymer was used as a compatibilizer. The shear viscosity of the ternary blend is slightly lower than that of the binary blend. The morphology of the dispersed TLCP phase varies between droplets and oriented fibrils when the drawing is weak and is highly correlated with changes in tensile properties. The optimum die exit temperature (280°C) provides a more uniform morphology and more fibril shapes which are associated with the increased tensile properties. The die exit temperature effect still exists when the draw ratio is high. In all cases, it is manifest that, whenever applicable, extension is a decisive factor in the deformation of the dispersed TLCP droplets, which is necessary for significant improvements in the mechanical properties.

Structure development during flow of ternary blends of a polyamide (nylon 66), a thermotropic liquid crystalline polymer (poly(ester amide)) and a functionalized polypropylene

It is shown that a fibril structure of a thermotropic liquid crystalline polymer (TLCP)(poly(ester amide)) can be developed in the shear flow field of a thermoplastic matrix (polyamide, nylon 66) when the viscosity of the latter is lower than that of the former. The addition of a third component, a functionalized polypropylene (maleic-anhydride-grafted polypropylene, MA-PP) that interacts with both the matrix polymer (nylon 66) and the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP by acting as a compatibilizer at the interface. Morphological observations have demonstrated the significance of compatibilization in immiscible polymer blends. The compatibilizer brings about good adhesion at the interface, reduces the droplet size, and enables a finely dispersed liquid crystalline polymer to be deformed by shear flow without strong elongation, even when the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties of the ternary blends are increased when a proper amount of MA-PP is added. This is attributed to fine strand generation induced by the addition of MA-PP. Enhanced adhesion at the interface invokes better elongation in the ternary blends.

TLCP ternary blends for in situ composites : In situ compatibilizer

It is experimentally shown that an in situ compatibilizer for the thermotropic liquid crystalline polymer blend can be generated in the extrusion process and that the compatibilizing action by the maleic anhydride-attached ethylene–propylene–diene terpolymer (MA–EPDM) in the blend of nylon46 and a thermotropic liquid crystalline polymer (polyesteramide) is due to the graft copolymer produced by the chemical reactions between the MA group of EPDM and functional groups of nylon46 and polyesteramide. This is apparent from the 1H-NMR spectra and TGA thermograms. Produced compatibilizers act at the interface to enable better adhesion, better stress transfer, and, hence, deformation of the dispersed phase into fine fibril shape even when the viscosity of the matrix is lower than that of the dispersed phase and the draw ratio is quite low (ca. 1.6).

Structure development of TLCP ternary blends during biaxial elongational flow

This study demonstrates the important role of the compatibilizer in blown films of a ternary blend of a thermotropic liquid crystalline polymer (TLCP (a poly(ester amide)), dispersed phase), a polyetherimide (matrix), and a poly(ester imide) (PEsI, compatibilizer). We investigated the morphology of the blown films via transmission electron microscopy and scanning electron microscopy, as well as optical microscopy. A stripe structure of TLCP phase was observed in the blown film, which evidently showed unequal biaxial deformation of the dispersed phase. The compatibilizer helped to deform the dispersed phase in the hoop direction as well as in the flow direction. It was evident that the amount of compatibilizer played a very important role in the dispersion and the deformation of the TLCP phase. It was found that 0.6 wt% of the compatibilizer was the optimum amount when 10 wt% TLCP was included. Coalescence of the TLCP phase was observed when excessive amount of the compatibilizer was used, resulting in a larger dispersed-phase size. The crystalline structure of the dispersed phase did not vary with the compatibilizer. A qualitative explanation of the effect of the compatibilizer on the deformation of the dispersed droplets is given based on simple droplet elasticity and interfacial tension.

A new model for rapid evaluation of the degree of long-chain branching in polymers

Abstract A new model is proposed for rapid evaluation of the degree of long-chain branching in polymers, which correlates the intrinsic viscosity and the molecular weight. Intrinsic viscosity is expressed as a simple inverse tangent function of molecular weight. The model is based on the observation of rheological behaviour of polymer melts and solutions. It can describe the intrinsic viscosity behaviour over a wider range than the Mark-Houwink equation. This model does not use trial and error procedure to decide the threshold molecular weight where the intrinsic viscosity starts to deviate from the Mark-Houwink relation. Calculation by the proposed model of the long-chain branching frequency of low density polyethylene shows good agreement with experimental results in the literature.