Markku T. Heino

Compatibilization of polyethylene terephthalate/polypropylene blends with styrene-ethylene/butylene-styrene (SEBS) block copolymers

Blends of polyethylene terephthalate (PET) and polypropylene (PP) at compositions 20/80 and 80/20 were modified with three different styrene–ethylene/butyl–ene-styrene (SEBS) triblock copolymers with the aim of improving the compatibility and in particular the toughness of the blends. The compatibilizers involved an unfunctionalized SEBS and two functionalized grades containing either maleic anhydride (SEBS-g-MAH) or glycidyl methacrylate (SEBS-g-GMA) grafted to the midblock. The effects of the compatibilizers were evaluated by studies on morphology and mechanical, thermal and rheological properties of the blends. The additon of 5 wt % of a SEBS copolymer was found to stabilize the blend morphology and to improve the impact strength. The effect was, however, far more pronounced with the functionalized copolymers. Particularly high toughness combined with rather high stiffness was achieved with SEBS-g-GMA for the PET-rich composition. Addition of the functionalized SEBS copolymers resulted in a finer dispersion of the minor phase and clearly improved interfacial adhesion. Shifts in the glass transition temperature of the PET phase and increase in the melt viscosity of the compatibilized blends indicated enhanced interactions between the discrete PET and PP phases induced by the functionalized compatibilizer, in particular SEBS-g-GMA.

Reinforcement of biodegradable poly(ester-urethane) with fillers

Abstract Two novel poly(ester-urethanes) (PEUs: PEUa and PEUb) were reinforced by blending in a batch mixer with organic and inorganic fillers of different particle sizes and shapes. In most experiments the filler contents were 0, 5, 15, 30, and 50 wt.%. In general, both the particulate and fibre-like fillers increased the stiffness almost linearly with increasing filler content, but the tensile and impact strengths and strain at break showed a downward trend. Exceptionally, improvements in tensile strength were achieved with glass fibre, as expected, and, surprisingly, also with some blend compositions containing silicate-type fillers. In addition, slightly improved impact strength was achieved with a small amount of fine talc. Dynamic-mechanical thermal analysis confirmed the reinforcing effects and showed some slight changes in the glass transition temperature of the PEU. Scanning electron microscopy studies on the morphology revealed relatively good mixing and contact between all the fillers and PEU.

Use of oxazoline functionalized polyolefins and elastomers as compatibilizers for thermoplastic blends

Oxazoline functionalized polypropylene, polyethylene, ethylene propylene copolymer (E/P), and styrene ethylene/butylene styrene copolymer (SEBS) were studied as compatibilizers in blends of polyolefins with polyesters and polyamides. The blends investigated were polypropylene/polyamide 6, polypropylene/polybutylene terephtalate, and polyethylene/polyamide 6, with engineering thermoplastic contents of 30 wt %. The blends were prepared in a twin-screw midiextruder, and injection molded with a mini-injection molding machine. The effect of compatibilizing on the morphology and mechanical properties of the blends was of interest. Compatibilization substantially improved the toughness of all tested blends. Their strength and stiffness remained at the level of the binary blends when polypropylene or polyethylene based compatibilizers were used, but slightly decreased with other compatibilizers. Morphological studies showed that the particle size was reduced, and the adhesion of the dispersed phase to the matrix improved by compatibilization. The effect of unfunctionalized polyethylene, polypropylene, E/P, and SEBS was also studied to compare the compatibilizers with them.

Studies on fracture behavior of tough PA6/PP blends

Fracture toughness of injection-molded PA6/PP blends compatibilized with SEBS-g-MA was studied using deeply double-edge notched tension (DDENT) specimens according to the essential work of fracture procedure. The fracture mechanical studies also included tensile impact tests on the DDENT specimens and characterization of the fracture surfaces by electron microscopy. The results were compared with those of traditional tensile tests and Izod impact tests on single-edge notched samples, and the sensibility of the methods was evaluated. Effects of sample position, ligament length, testing direction, and test speed were studied as well. It was found that the essential work of fracture concept, earlier applied to thin sheets, can also be applied to injection-molded tough blends. High deformation of the skin may, however, interfere with the measurements and cause a “tail” in the load-deformation curves. The plastic work of fracture (wp) was found to correlate with the impact strength, and thus, it described the toughness. The highest values for work of fracture were recorded for the compatibilized blend with a PA6/PP ratio of 80/20. The essential work of fracture (we) in turn increased with increasing PA6 content and behaved like tensile strength. The test speed was found to affect the fracture behavior substantially: differences between the materials were more pronounced in high-speed tensile impact tests, which revealed signs of cavitation in addition to large-scale plastic deformation for the tough PA6-rich blend compositions.

Studies on blends of a thermotropic liquid crystalline polymer and polybutylene terephthalate

SummaryStructure-property relationships of blends of a thermotropic polyester-type main-chain LCP and polybutylene terephthalate (PBT) were investigated. LCP was melt blended with three different PBTs and the blends were processed by injection moulding or extrusion. Mechanical and thermal properties of the blends were determined and the blend structure was characterized by scanning electron microscopy (SEM). LCP acted as mechanical reinforcement for PBT and improved also its dimensional and thermal stability. The stiffness of PBT increased with increasing LCP content, but at the same time the blends became more brittle. In extrusion the orientation of LCP phases could be further enhanced by additional drawing, which led to significant improvements in strength and stiffness at LCP contents of 20–30 wt.-%.

Compatibilization of PP/PBT and PP/PA6 blends with a new oxazoline-functionalized polypropylene

SummaryAim of this work was to study the effectiveness of a novel oxazoline-functionalized polypropylene as a compatibilizer for PP/PBT and PP/PA6 blends. This polypropylene-based compatibilizer mixes well with the polypropylene and is capable of reacting with the carboxylic and amine end groups of PBT and PA6. Significant improvements in blend toughness were achieved without reduction in strength and stiffness. These effects were related to stabilized morphology of finely dispersed minor phase well attached to the matrix. The enhanced interfacial interactions between the two phases, in particular at high PBT content were evidenced by increased melt viscosity.

In-situ reinforced polypropylene blends

Blending with high-performance engineering polymers is a feasible way of upgrading the properties of commodity thermoplastics. The aim of blending is often to improve the mechanical strength or toughness or, for example, the thermal resistance of the matrix polymer. Addition of conventional thermoplastics such as polyamides or polyesters, to polyolefins improves the properties, however, only to a relatively small extent. Completely different phenomena are instead achieved when thermotropic main-chain liquid crystalline polymers (LCPs) are used.

Effect of viscosity ratio and blending conditions on the morphology of LCP/PP blends.

ABSTRACT Blends of thermotropic liquid crystalline polymers (TLCPs) and thermoplastics consist generally of two separate phases, since the polymers are immiscible. The dispersed LCP phase can exist in the form of spheres, ellipsoids, platelets or fibrils depending on some material properties and blending conditions. Morphology of immiscible polymer blends is influenced by several different parameters like blend composition, viscosity ratio, elasticity ratio, interfacial tension, temperature, residence time, mixing intensity, draw ratio etc. In this paper, the effect of viscosity ratio on the blend morphology was studied by blending two different LCPs (Vectra A950 and Rodrun LC-3000) with five polypropylenes. Viscosity ratio was varied from 0.1 to 3.6. Viscosity ratio was found to have a clear effect on the dispersion and fiber formation of the LCP component. Good fiber formation was obtained with a viscosity ratio from about 0.5 to 1. The effect of blending equipment and conditions were studied with the blends of Vectra A950 and two polypropylenes. The blends prepared by counter- and co-rotating twin screw extruder and Buss co-kneader exhibited three different morphologies. Special attention was paid to the effect of shear forces on the dispersion and orientation of LCP, while deformation caused by elongational drawing was minimized. The screw speed of the twin screw extruders had only minor effect on blend morphology. The slight differences in morphology found after 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 knowing the viscosity ratio at processing in the actual processing conditions is of great importance.