Compatibilization of blends of polyethylene with a semirigid liquid crystalline polymer by PE‐g‐LCP copolymers

Abstract

The blends of thermoplastics with liquid crystalline polymers show, in general, poor properties because of the lack of adherence between the two phases. The use of ad hoc synthesized copolymers containing the monomer units of the two polymers has been recently considered by some of us for blend compatibilization, and the results appear promising. In this work, new PE‐g‐LCP copolymers, prepared either by the synthesis of the LCP in the presence of a functionalized PE, or by reactive blending of the latter polymer with preformed LCP, have been employed as compatibilizing additives for blends of PE with a semirigid LCP. The morphology and the rheological and mechanical properties of the ternary blends, compared with those of samples without compatibilizers, or containing conventional maleic anhydride grafted PE, indicate that the PE‐g‐LCP copolymers do in fact lead to an improvement of interfacial adhesion, both in the melt and in the solid state, as well as to a modest enhancement of the mechanical properties. The results may be rationalized considering that the PE‐g‐LCP copolymers used by us consist of fairly short PE backbones with LCP grafts of various length. The molecules with longer LCP branches are thought to become mixed at the surface of the LCP particles and to give rise to fairly weak interaction with the PE matrix. It is argued that new PE‐g‐LCP copolymers synthesized from higher molar mass functionalized PE samples might show much better compatibilizing performance.

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

“…It may be noted that the addition of SBH to A1100 lowers the viscosity of the latter, as has been shown previously. 8 The analysis of the curves in Figure 6 demonstrates that the addition of 4 wt % Escor or COP into this binary blend increases slightly the viscosity in the lower shear rate range. This increase, which is just a little higher for COP, is an indication that the adhesion between the blend components is improved in the presence of the compatibilizers.…”

“…The study of the rheological behavior of the pure components of the blends, namely, A1100, Eltex, Escor, and SBH, published elsewhere, 7,8,19 shows that the viscosity of Eltex is higher than that of A1100, that Escor displays a lower viscosity than that of the two HDPE samples, and that SBH has the lowest viscosity in the whole shear rate range. The melt viscosity of the binary (50/50 w/w) blends A1100/Escor and Eltex/Escor is intermediate between the values for the pure components.…”

“…These studies have shown that maleic anhydride-grafted PP (PPMA) or acrylic acid-functionalized PP (PPAA) can improve the interfacial adhesion in PP/LCP blends, and an enhancement of the tensile modulus, tensile strength, and surface finish was observed. [1][2][3][4][5][6] For blends of PE with a semiflexible LCP, compatibilized with two samples of maleic anhydride-grafted PE (PEMA), 7,8 the enhancement of the mechanical properties was generally modest. Also, in this case, the enhancement of some of the blend properties was attributed to the promotion of specific polar interactions between the components.…”

“…The approach of using compatibilizers consisting of graft copolymers made up of segments whose chemical structure is similar 5 or identical 8,[11][12][13] to that of the polymers being blended was applied recently to the modification of polyolefin/LCP blends. The compatibilization mechanism involves the migration of the copolymer molecules to the interphase and the penetration of each copolymer segment into a structurally alike phase.…”

“…Recent investigations [1][2][3][4][5][6][7][8] have dealt with the preparation and the characterization of blends of polypropylene (PP) or polyethylene (PE) with liquid crystalline polymers (LCPs) containing different commercially available compatibilizers. These studies have shown that maleic anhydride-grafted PP (PPMA) or acrylic acid-functionalized PP (PPAA) can improve the interfacial adhesion in PP/LCP blends, and an enhancement of the tensile modulus, tensile strength, and surface finish was observed.…”