Preparation And Characterizations Of Novel Polypropylene/Seaweed Fibre (PP/SW) Composites

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?and 60rpm to avoid fierce thermal decomposition of SW fibre during extrusion. PP/SW composites could be easlier moulded in-mjection maschine, the ideal moulding parameters in this thesis are:injection temperature=180?, rotation speed of screw=60rpm, injection pressure=moulding pressure=60bar, moulding temperature=60?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.