P. L. Magagnini

Relationships between mechanical properties and structure for blends of nylon-6 with a liquid crystal polymer

Abstract Mechanical properties of blends of nylon-6 with a liquid crystal copolyesteramide (LCP) are presented. The improvement of the elastic modulus increases with increasing the draw ratio. Fibrils of LCP are evident when the draw ratio >40. The moduli are lower than those predicted by the theory of short-fibre oriented composites probably because of poor adhesion between the two phases and to incomplete fibrilation of the LCP particles.

Compatibility of blends of poly(butylene terephthalate) and liquid crystal polymers: a DSC study

Abstract A calorimetric study of blends of poly(butylene terephthalate) (PBT) with two liquid crystal polyesters, one aliphatic-aromatic poly(biphenyl-4,4-ylene sebacate) (PB8) and the other wholly aromatic (Vectra B 950), has been made for the prime purpose of obtaining information on the interphase. The dependence of the transition temperatures and enthalpies on blend composition, together with examination of the chemical interactions occurring at high temperature at the interface, showed that the compatibility between PBT and Vectra is much lower than that between PBT and PB8. Electron scanning microscopy confirmed this conclusion.

Processing and Properties of Polycarbonate/Liquid Crystal Polymer Blends

Abstract Rheological and mechanical properties, structural characteristics, extrusion and injection molding behavior of blends of polycarbonate (PC) with a thermotropic, wholly aromatic copolyesteramide have been investigated. The processability of polycarbonate is remarkably improved by addition of small contents of liquid crystal polymer. All the flow curves of the blends lie between those of the pure components. In the processing conditions adopted, the LCP particles are easily elongated in the flow direction. In this direction the elastic modulus rises remarkably with LCP content. The modulus-composition curve is, however, lower than that expected on the basis of an additive rule due to the incompatibility and poor adhesion between the two phases. Finally, injection molding of this extrusion grade PC has been easily performed by adding small contents of LCP. The impact strength values of the injection molding samples of these blends are only slightly lower than that of the pure PC.

Crystallization behaviour and thermal stability of HDPE filled during polymerization

Abstract High density polyethylene, (HDPE) filled during the polymerization process with chalk and marble powder (degree of filling 5–22% w/w) has been investigated by means of DSC, polarizing microscopy and thermogravimetry. The crystallization behaviour of the filled polyethylene samples has been investigated under non-isothermal conditions at different cooling rates. It has been found that the presence of the fillers leads to an increase in the temperature of crystallization, the temperature of half-crystallization and the crystallization rate coefficient of the polymer, but the degree of crystallinity and the Avrami exponent do not change significantly. Spherulites with smaller dimensions are obtained in filled polyethylenes for both isothermal and non-isothermal crystallization carried out at small cooling rates. The results have been interpreted in terms of an increase in the crystallization rate of filled polyethylenes, due to the nucleating role of the fillers, without changing the mechanism of the non-isothermal crystallization. The thermal stability of the filled polyethylenes has been estimated from parameters of non-isothermal degradation in air. It hardly changes or only slightly increases compared with unfilled PE.

Synthesis and characterization of a PE‐g‐LCP copolymer

The possibility of reinforcing polyethylene (PE) by blending it with a liquid crystalline polymer (LCP) rests on the successful improvement of phase compatibility and interfacial adhesion of these two structurally unlike polymers. The approach that is being considered in our laboratories consists of the synthesis of PE-LCP block or graft copolymers and of their use as compatibilizing agents for PE/LCP blends. In this work, the melt polycondensation of sebacic acid (S), 4,4-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) has been carried out at temperatures up to 280°C in the presence of an oxidized low molar mass PE sample containing free carboxylic groups (PEox), with the main scope of demonstrating that a PE-g-LCP copolymer may be synthesized by this route. The polycondensation product has been fractionated by successive extractions with boiling toluene and xylene. The soluble fractions and the residues have been characterized by IR and NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TG, DTG), and scanning electron microscopy (SEM). The extractions and the analyses have been repeated on a PEox/LCP blend prepared by melt mixing PEox and preformed LCP (SBH 112, by Eniricerche). The results show that, whereas for the blend a fairly clean separation of PEox and SBH can be obtained by solvent extraction, this is not so for the polycondensation product. All analytical procedures concordantly show that a PEox-g-SBH copolymer has, in fact, been obtained. In effect, both PEox and SBH chain segments are present, with different relative ratios, in all fractions of the polycondensate. Moreover, a fairly quantitative esterification of the PEox carboxyl groups has been shown by IR analysis to take place in the adopted conditions. Preliminary morphological investigations carried out by SEM have shown that the addition of the synthesized graft copolymer into HDPE/SBH blends leads to an improvement of the interfacial adhesion.

Reactive blending of a functionalized polyethylene with a semiflexible liquid crystalline copolyester

Reactive blends (50/50 w/w) of a low molar mass polyethylene containing free carboxylic groups (PEox) and a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2, by Eniricerche) have been prepared at 240°C in a Brabender mixer, in the presence of Ti(OBu) 4 catalyst, for different mixing times (15, 60, and 120 min). In order to prove the formation of a PE-g-SBH copolymer, the blends have been fractionated by successive extractions with boiling toluene and xylene. The soluble fractions and the residues have been analyzed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry (TG and DTG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). All analytical procedures concordantly show that PE-g-SBH copolymers with different compositions, arising from differences of either the number of PEox carboxylic groups entering the transesterification or the length of grafted SBH branches, are formed as a result of blending. Depending on the relative content of PE and SBH segments, the copolymers dissolve in the solvents, together with any unreacted PEox, or remain in the residues, together with neat SBH. Qualitative IR analyses and quantitative TG measurements have shown that the amount of copolymers increases strongly with the mixing time. Preliminary SEM observations indicate that the unfractionated products of the reactive blending carried out with long (120 min) mixing times lead to improved interfacial adhesion and phase dispersion when added to PE/SBH blends.

Effect of the components' molar mass and of the mixing conditions on the compatibilization of PE–LCP blends by PE‐g‐LCP copolymers

The rheology, morphology, and mechanical properties of blends of high-density polyethylene (HDPE) with a semiflexible liquid crystalline copolyester (SBH) were studied in order to assess the compatibilizing ability of added PE-g-SBH copolymers, and its dependence on the molar mass of the PE matrix, and on the technique used for blend preparation. The PE-g-SBH copolymers were synthesized as described in previous articles, either by the polycondensation of the SBH monomers in the presence of a functionalized PE sample containing free carboxyl groups, or by reactive blending of the latter polymer with preformed SBH. Two samples of HDPE having different molar masses, and two samples of SBH with different melt viscosity and different microstructure, were used for preparing the blends. The two components and the compatibilizer were either blended in a single batch or used to prepare binary master blends to which the third component was added at a later stage. The results indicate that the PE-g-SBH copolymers do, in fact, compatibilize the PE–SBH blends and that the effect is more pronounced with the lower molar mass PE matrix and with the SBH sample having lower viscosity. The experiments carried out on blends prepared with different techniques show that the compatibilizing ability of the graft copolymer is improved if the latter is first blended with either of the two main components.

Morphology and rheology of HDPE/LCP blends compatibilized by a novel PE-g-LCP copolymer

A novel graft copolymer (PE-g-LCP) consisting of polyethylene (PE) backbones and liquid crystalline polymer (LCP) branches was synthesized via reactive blending of an acrylic acid-functionalized PE (Escor 5000 by Exxon) with a semiflexible LCP (SBH 1 : 1 : 2 by Eniricerche S.p.A.). The crude reactive blending product (COP) was shown by investigation of the fractions soluble in boiling toluene and xylene and of the residue to contain unreacted Escor and SBH, together with the graft copolymer forming the interphase. The compatibilizing activity of COP for PE/SBH blends, compared to that of pure Escor, was investigated using two PE grades. The COP addition into 80/20 PE/SBH blends caused a much stronger reduction of the SBH droplet dimensions and morphology stabilization than did that of pure Escor. The rheological behavior of the samples showed that COP leads to a slight increase of interfacial adhesion in the melt as well and that the effect is more pronounced when lower molar mass PE grade is used as the blend matrix. Melt-spinning tests demonstrated that deformation of the SBH droplets into highly oriented fibrils can be obtained for the blends of lower molar mass PE, compatibilized with small amounts of the novel PE-g-SBH copolymer.