Polyolefin Materials: Structure Of Impact Polypropylene Copolymer And Properties Of Conductive Composites

As a kind of reactor alloy, impact polypropylene copolymer (IPC) is of fastest in development, greatest in profit and more in yield in polypropylene family for volume-produce products. Due to complex composition, chain structure, phase morphology and production technology, this novel polypropylene has attracted attention of academic and industrial fields. In this study, structure and properties were investigated and structure model was established. All of these have supplied technical support for controlling composition and microstructure and adjusting all sorts of properties of the materials.Self-limited temperature heating strip is only a volume-produced product in heating elements for polyolefin conductive composites. The heating object as narrow strip type is only used in accompanying heat and heat preservation at 220 V, because of limitation of the power. Development and study for big power heating element, e.g. heating pipe, could exploit application field of the self-limited temperature heating materials and promoted the development of the brainpower heating material in low temperature heating field. In addition, in owe to fit together the heating strip and the pipe with metal material were into use, it is necessary to solve the difficulties in cold start and run in winter for diesel engine.Crystal morphology and behavior, crystallite size and phase morphology for two impact polypropylene copolymer with the same ethylene content, rubber content, relative molecular weight and molecular weight distribution through different catalyst systems in a same unit but obviously different toughness were investigated by polarized microscope (PLM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), scanning electric microscope (SEM), dynamic mechanical analysis (DMA) and atomic force microscope (AFM). Differences between structure of condensed state and properties were analyzed, direct reason of bad toughness for IPC was ascertained, and the action of long sequence ethylene-propylene block copolymer was elucidated according to the experimental data.Crystallization morphology and behavior, Crystallite size and crystallinity ofIPC-A and IPC-B were similar, which show crystallization integrality and ability of both IPC are approximate. Aggregation of disperse phase granules happens in the process of injection mold for IPC pellets. According to the micromorphology, the influence of temperature and mixing before and after the process on phase structure and a model concerning disperse phase growth in the process of injection mold was established. The lower the interface tensility between disperse phase and matrix is, the poorer the compatibility and the more the granules congregating. The disperse phase with large size presents because of the poor compatibility, which is considered as a main reason for poor toughness. Therefore, the disperse phase exhibits a complex phase structure, outer layer is a soft ethylene-propylene random copolymer (that is ethylene-propylene rubber, EPR), and the interior contains hard polyethylene crystal regions with different shape and ununiform distribution. These result in formation of a complex concealment structure.Factors influencing the impact toughness of two IPC were studied by temperature gradient extraction fractionation (TGEF), nuclear magnetic resonance (NMR), DSC and infrared spectrumetry-fouorier transform (FTIR). The results provided some experimental evidence that the lack of ethylene-propylene segmented copolymer with long crystallizable sequences leads to the coarsening of disperse phase in the IPC and poor toughness of the material. According to the analytic results of composition and chain structure, phase composition of the IPC was identified and analyzed, and a model of phase structure was proposed to describe the phase structure of both IPC heterophase systems and the action and difference of E-b-P in the IPC.On the other hand in this dissertation, influences of carbon black (CB) content on resistance-temperature characteristic and heating behavior for high density polyethylene (HDPE)/CB conductive composites with self-limited temperature were studied. The CB content in the composite with the highest heating temperature corresponds to upper limitation of the percolation region. Response time of heating material shortened obviously with increasing of voltage, and on the other hand the output power and dissipation power of the material approach equilibrium easily, embodiment in heating elements was quick in rising temperature.Moreover, the micromorphology of CB and the composites was observed byusing transmission electric microscope (TEM) and SEM respectively. The relationship among percolating behaviors, electrothermal characteristics and special net structure/morphology were investigated. The results show that a network of the CB aggregates formed, which endows the good conductive and mechanical properties.For the heating pipe with self-limited temperature, a novel heating element that could produced continuously by polymer composites was developed in the work, and its electrothermal characteristics was investigated. The equivalent circuit model and electric current model of heating pipe and strip were established. The testing results of the heating temperature, heat-work conversion efficiency and use longevity of the heating pipe show that it is possible for the foundational element of brainpower type becoming an applied heating resource for low temperature heating except using for concomitance heat, heat preservation and substituting for the metal heating elements in many fields. Furthermore, heating strip using at safe voltage with self-limited temperature was developed.In the aspect of application, according to the structure, shape and work mechanism for every parts of supplying oil systems, main reasons of cold start difficulty for the diesel vehicle in winter were analyzed. A kind of combining heater was obtained by assembling heating strip and pipe with self-limited temperature and corresponding electrothermal characteristics were studied. Furthermore the heater in diesel truck and cold start testing was done in winter. The results show that this combining heater is very effective for cold start and normal run of diesel vehicle, indicating the self-limited temperature heating material and elements of polymer composites, are feasible to use in cold start for vehicle. In civil aspect, self-limited temperature heater was made of the heating pipe with self-limited temperature, which used as water heater. On the other hand, heating pad was made of the heating strip with self-limited temperature, and was used to warm oneself and health care.