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Title: Preparation and Properties Research of the Polyamide 6/Functionalized Elastomer/ Montmorillonite Nanocomposites Writer: Sanxiong He Supervisor: Wei Wu Abstract:A styrene-ethylene/butadiene-styrene triblock copolymers (SEBS) was functionalized respectively with glycidyl methacrylate (GMA) and maleic anhydride (MAH). PA6-based composites were prepared using the functionalized SEBS as a toughener, or adding polycarbonate at the same time, and one commercial organo-montmorillonite (OMMT) served as reinforcing filler. GMA or epoxy resin (EP) was used as a compatibilizer for the composites. Influence of the type of functional group, grafting degree, the contents of the filler and compatibilizer, and the micro-crosslinking among the components on the morphology, the structure and properties were investigated by all kinds of methods,e.g. XRD, SEM, TGA, DSC, FTIR, Molau test, mechanical properties test and rheology. Firstly, PA6/OMMT nanocomposites were prepared by means of melt blending. When the content of OMMT was 4wt%, the nanocomposite has a higher tensile strength, flexile strength and flexile modulus. But the impact strength was decreased. The exfoliated behavior was confirmed by XRD and TEM. PA6/OMMT blend could scatter uniformly in the formic acid solution without sedimentation and phase separation. The SEBS-g-GMA and SEBS-g-MAH were respectively prepared using GMA and MAH though melt extrusion. The grafting degrees were respectively 2.39% and 1.2%, which were decided by titration. SEBS-g-GMA and SEBS-g-MAH were used to prepare PA6/elastomer/OMMT nanocomposites. The mechanical properties, crystallization behavior, thermal stability and the morphology were investigated. The PA6/elastomer/OMMT had mechanical properties balanced between those of PA6 and PA6/elastomer blends. Brittle-ductile transition could happen when the content of elastomer was 30wt%, and the toughness improved rapidly. The tensile strength and flexile strength are above 90% of pure PA6. There is a clear trade-off between stiffness/strength versus toughness/ductility. SEBS-g-GMA and SEBS-g-MAH had the different morphology in the composites. The particle size of SEBS-g-GMA is much larger than that of SEBS-g-MAH, due to the possible crosslinking with PA6. The toughening efficiency of SEBS-g-GMA was much lower than SEBS-g-MAH. The elastomer particle size decreased at low OMMT loading because OMMT could prevent dispersed phase coalescence. With increasing OMMT content, OMMT weakened the interfacial adhesion between PA6 and functionalized elastomer leading to an increase in the elastomer particle size and a decrease in the impact strength of the composites. PA6-based composites toughened by SEBS-g-GMA did not dissolve in the formic acid, and suspended in the upper of the tube. A milky and colloidal suspension was observed for PA6-based composites toughened by SEBS-g-MAH. The elastomer particle size clearly decreased with increasing MAH content. The impact strength remained almost constantly. SEBS-g-GMA and SEBS-g-MAH both decreased the melt temperature, and hindered the crystallization of the composites. The ternary composites were prepared by two different blending sequences (N1 and N2). The method N1 means PA6, elastomer, and OMMT were blended simultaneously. The method N2 means that the ternary composite was produced through the premixing of PA6 and OMMT first and then melt blending with elastomer. The composite (N2) has better mechanical properties. The notched impact strength of the one composite (N2) was 122% higher than that of the other composite (N1), even for the same formulation. For the ternary composites prepared via method N1 with the addition of GMA or EP, the tensile strength, flexural strength, and flexural modulus just slightly decreased, whereas the impact strength and elongation at break were significantly enhanced. The chemical reaction between PA6, SEBS-g-MAH, and the compatilizer could enhance the viscosity, storage modulus, and loss modulus. The blends couldn’t dissolve in formic acid solution. The impact strength of PA6/SEBS-g-MAH/PC composite improved greatly compared with that of PA6/SEBS-g-MAH composite. Epoxy resin was used to improve the compatibility between PA6 and PC. Then adding EP (1wt%) to PA6/SEBS-g-MAH/PC alloy, the notched impact strength of alloy is 55.61kJ/m2 (increasing 313.2% as that of pure PA6) and the elongation at break is 306.4% (increasing 625.2% as that of pure PA6). Novel toughening alloy is gained with outstanding mechanical properties. In addition, the adding of OMMT improved the tensile and flexile properties of the composite remarkably. The interphase boundaries became increasingly indistinctive with the adding of EP, and the tensile and flexile strength increased. The notched impact strength increased firstly and then decreased. Polycarbonate would improve the thermal stability of the composites. The thermo-decomposing temperature rises obviously due to the crosslinking caused by the compatilizer EP.
Title:Preparation and Properties of Polypropylene/Natural Seaweed Fiber Composites Writer: Lixing Luan Supervisor: Wei Wu Abstract:In this thesis, seaweed fibre (SW) is adopted as reinforcing fibre for polypropylene matrix (PP) for the first time, the novel polypropylene/seaweed fibre (PP/SW) composites is prepared. After optimization of the parameters during “melt extrusion-injection moulding”, PP/SW composites are successfully prepared by traditional processing equipments. The mechanical, thermal dynamical, crystallization, dynamic rheological properities as well as thermal decomposition and combustion progressions are well characterized. The model for phase structure transition of PP/SW composites is proposed as well as the solid-phase flame retardancy of SW fibre for PP matrix. Taking consideration of the influence of SW content and type of extruder on the compounding, the processability of PP/SW composites is well evaluated. Based on the results, PP/SW composites are successfully prepared in a twin-screw extruder, which maintain the thermal stability of SW fibre as well as realize fine dispersion within PP matrix. TPU could act as efficient PPA (Polymer Processing Aid) in compounding that eliminates melt-fracture phenomena in PP/SW melt. However, SW content should below 50wt% in order to keep enough melt flow rate. Compounding temperature and rotation speed of screw should be strictly controlled below 185°C and 60rpm to avoid fierce thermal decomposition of SW fibre during extrusion. PP/SW composites could be easlier moulded in injection maschine, the ideal moulding parameters in this thesis are: injection temperature=180°C, rotation speed of screw=60rpm, injection pressure=moulding pressure=60bar, moulding temperature=60°C and cooling time=45s. The reinforcing effect of SW fibre for PP matrix is evaluated by mechanical characterization. According to the properties, surface alkalization is could remove impurities from SW fibre thus improve its stiffness. However, the poor adhesion between PP matrix and SW fibre limits the properties of PP/SW composites; compatibilization and lubricating are of necessity. The lubricating effects are classified into “inner effect” and “outter effect” in this thesis. Based on the results, MAPP as “inner lubricant” and CESA as “outter lubricant” can both enhance the mechanical properties of PP/SW composites, which is in agreement to the raing of storage modulus and loss modulus from DMA test. Diversed effects on the damping factor state their difference in lubricating mechanisms, the stiffness is raised by MAPP while CESA improved the elasticity of PP/SW composites. SW fibre accelerates the process of crystallization of PP matrix, but reduces its degree of crystallization. With either MAPP or CESA, the degree of crystallization is improved which proves the heterogeneous nucleation effect of SW fibre for PP matrix. Dynamic rheological characterizations provide important information on the transition of phase structure for PP/SW composites. The wide linear viscoelastic region signifies fine dispersion of SW fibre, as well as feasibility of compounding and moulding process. A formation of “Newton Plateau” indicates the establishment of physical network between PP matrix and SW fibre. CESA remarkably changes the phase structure of PP/SW composites, and achieve a higher apparent yield stress; while MAPP leads to slight influence on the rheological properties. With “time-temperature superposition principle”, it can be concluded that CESA transforms PP/SW composites from heterogeneous system into homogeneous system. Within studied temperature region, no evidence for phase-separation is traced after the addition of CESA. Moreover, the thermal decomposition and combustion behaviour of PP/SW composites are well studied in this thesis. With high thermal stability, SW fibre could delay the thermal decomposition of matrix. SW fibre also acts as a solid-phase flame retardant in the composite, remarkably reduces the combustion parameters of PP matrix. Higher uniformity in the composite is beneficial for SW fibre’s retarding effect, the total heat release and peak heat release rate are declined by 25% and 75%, respectively. However, SW fibre hardly reduces the flammability of PP matrix. To conclude, PP/SW composites possess favourable processability with satisfying mechanical properties for normal usage. The heat and flame resistance of PP/SW composites is greatly higher in comparsion to PP matrix, thus promises its potential in applications. The lubricating mechanism for PP/NVF composites and SW fibre’s interesting flame retarding effect found in this thesis could promote related research.
Title:Preparation and Properties of Wood Flour-Filled Polypropylene Composites Writer: Ru Wang Supervisor: Wei Wu Abstract:In this paper, PP and wood fiber with 80 meshes were choosed to prepare for PP/WF Composites. Research showed that tensile strength, flexural strength, impact strength, elongation at break was decreased with increased wood fiber content except flexural modulus which was increased. Addition of wood fiber brings faster crystallization, lower crystallinity, and poorer thermostability. Three maleated compatibilizer were used in this paper to improve the surface bonding of PP and wood flour. Research showed that PP-g-MAH is the best compatibilizer in this system and mechanical properties exhibited a great reinforcement by 10% adding. Alkali treatment was used to treat wood fiber. Result showed that alkali treatment for wood fiber is beneficial for mechanical properties, flowability, thermostability, but make water absorption increased. At last, added OMMT in PP/WF system. Research shows that OMMT is good for mechanical properties and thermostability of PP. The layer distance is enlarged after adding in PP which was found by XRD. PP-g-MAH can be used as compatibilizer for both of PP/OMMT and PP/WF. Tensile strength, flexural strength, flexural modulus were increase except impact strength when PP-g-MAH was added in PP/OMMT system.OMMT was peeling in PP if 3% PP-g-MAH was used which was researched by XRD. But OMMT brings PP/WF composites poorer mechanical properties. If OMMT and PP-g-MAH both were added in PP/WF system, then a better thermostability was produced.
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