Studies Of The Toughening And Strengthening Effect Of Styrene-Butadiene Rubber/Nano-CaCO₃ Complex Powdered Rubber On Polypropylene

Recently, many researches have focused on the studies of common polymer materials with high performance and multiple functions. In this thesis, a new kind of rubber powder with "salami" structure (RPS) was prepared by spray drying method. The PP/RPS ternary composites were prepared by melt blending method. The influences of the viscosity ratio, of the RPS with a series of styrene-butadiene rubber/nano-CaCO3 ratio and the RPS with different sodium benzoate content on the mechanical properties, crystallization properties and rheological properties of the composites were systematically investigated. The toughening mechanism of PP/RPS ternary composites was also studied. The RPS complex powdered rubber was prepared by spray drying the mixture of styrene-butadiene rubber latex and nano-CaCO3 slurry. yRPS (RPS with benzoate) and nRPS(RPS without benzoate) were also prepared. By adding different ratio of styrene-butadiene rubber latex and nano-CaCO3 slurry, a series of yRPS and nRPS were prepared. The Elastomeric Nano-Particle (DB-50 ENP) was also prepared by spray drying the styrene-butadiene rubber latex (DB-50 rubber latex).The relationship between the microstructure and the mechanical properties in PP/nano-CaCO3, PP/DB-50 ENP, PP/DB-50 ENP/nano-CaCO3 and PP/RPS systems was investigated. From the results it can be seen that the DB-50 ENP and nano-CaCO3 have a synergistic toughening effect on PP. The Izod impact strength of PP/RPS composites is not only higher than that of PP/ DB-50 ENP and PP/nano-CaCO3, but also higher than that of PP/DB-50 ENP/nano-CaCO3. TEM photograph shows that microstructure of PP/RPS composites is an "sea-island" structure with "salami" like structure in RPS, in which nano-CaCO3 particles are embedded in styrene-butadiene rubber particles at nano-size. The effect of preparing method on morphology is apparent, the microstructure of the PP/DB-50 ENP/nano-CaCO3 composites is different from PP/RPS, in which small amount of the CaCO3 particles are occluded by the DB-50 ENP, the most are dispersed in PP matrix. The impact resistance is affected by the volume fraction of rubber incorporated and the average surface-to-surface interparticle distance or the matrix ligament thickness of PP. The occlusion of nano-CaCO3 in elastomer is expected to increase the apparent volume fraction of the rubbery phase and decrease the average surface-to-surface distance between the elastomer particles, and thus the impact resistance of the matrix is improved. The effect of the DB-50 ENP/nano-CaCO3 ratio, of the sodium benzoate content in RPS and the viscosity ratio on the mechanical and the heat resistance properties of PP/RPS ternary composites with the same mass ratio was investigated. It can be seen that, with the increase of nano-CaCO3 content in the three RPS samples, RPS particle size decreases and the free nano-CaCO3 in PP increases. As a result, the tensile strength, the flexural strength and the heat resistance of the ternary system are enhanced, and the Izod impact strength is slightly improved. The crystallization temperature and the crystallinity of PP increase due to the nucleation effect of sodium benzoate, which contributed to the improvement of the rigidity and heat resistance of the composites. The sodium benzonate in RPS, also acting as a partitioning agent, can help decrease the particle size of the rubbery phase, and thus facilitate the toughening of PP. Low viscosity ratios are found to produce fine and uniform dispersion of RPS in PP, therefore the impact resistance of the composites is improved.The dynamic mechanical properties of PP, PP/nano-CaCO3, PP/ DB-50 ENP, PP/DB-50 ENP/nano-CaCO3 and PP/RPS were studied. The results show that the glass transition temperature of PP and DB-50 ENP changes little in all the samples. The storage modulus E' increases with the addition of nano-CaCO3, but decreases with the addition of DB-50 ENP or RPS. The loss modulus E'' of PP/RPS was higher than the PP/DB-50 ENP and the PP/DB-50 ENP/nano-CaCO3 in the whole temperature...