On In-Situ Fibrillation Of GEP/PO Blends And Their Morphology, Structure And Properties

Performance enhancement of general-purpose plastics (mainly polyethylene (PE) and polypropylene (PP)) is one of the most important research subjects in the field of polymer materials science and engineering at present and in the future. Blending modification is a major route. One of the promising methods is to generate some unique in-situ morphology such as fibers and plates during blending which can enhance the mechanical properties and add some functional properties to the original materials. This dissertation puts forward a simple, effective and clean process to improve the properties of general-purpose plastics.The in-situ fibrillation of the polyolefins (PO) based general engineering plastics (GEP)/PO blends during melt and solid state and their morphology, structure and properties were investigated in this thesis. A large quantity of valuable data and results were obtained, which is of importance to develop the theory for blending and alloying of polymer blends. The main results are:(I) Morphology and properties of GEP/PO in-situ microfibrillar blends obtained by extrusion-hot stretching-quenching methodThe in-situ microfibrillar blend (IMB) was prepared by melt extrusion-hot stretching-quenching process. The testing samples were injection molded at the processing temperature of matrix to avoid destroying the in-situ microfibers formed in the aforementioned process. The morphology and properties of polyethylene terephthalate (PET)/polyethylene (PE) blend were studied systematically.(1) The influences of different processing apparatus (extruder, injection machine and the extruder on HAAKE rheometer), the die geometry (slit die, sheet die and rod die) and the blend components on the fibrillation of GEP/PO blends were studied. The results showed that the extruder with a rectangular slit die is the best to form micorfibers, and the optimal polymer pair was PET/PE system.(2) At a fxied stretching ratio, The microfiber morphology characteristics were a function of PET content. With the increase of PET content, he microfiber became larger and its distribution wider with a relatively constant minimum fiber diameter. The tensile strength of PET/PEmicrofibrillar blend were increased by 100% compared to the common PET/PE blend with spherical dispersion. The microfibrillar blend showed a tough-brittle transition at 15 wt% of PET concentration, while the common blend still exhibit good toughness. This was caused by two different deformation mechanisms: there was slippage between the spherical particles and the matrix for the common blend, but no slippage between the microfibers and the matrix for the microfibrillar blend.(3) Fixing blend composition, the PET particles were deformed from spheres to ellipsoids, to rodlike particles and finally to well-defined microfibers when increasing the HSR from 1 to 47. The maximum and average diameters of PET particles reduced steadily while the minimum fiber diameter remained constant. The tensile modulus and strength of PET/PE blends were significantly enhanced with increasing hot stretching ratio. The ultimate elongation was greatly decreased with the increase of hot stretching ratio and there is a critical hot stretching ratio, above which the ductile-brittle transition occurred.(4) An expression for tensile strength calculation of the microfiber-contained blend was developed, which showed the relationship between the tensile strength of the microfibrillar blend and the parameters of the fiber reinforcement, matrix properties, material parameters, and especially processing conditions. Another model was attempted to predict the tough-brittle transition of the incompatible polymer blend containing the dispersed particles with a specific aspect ratio. In this model, the dispersed particles were regarded as the stress concentration body, and the matrix was divided into two regions: one closer to the particles is the craze and crack concentration region (A) which is responsible for the brittle fracture of the materials, the other region far away...