Structure-Property Relationships Of Impact Polypropylene Coplymer And Toughening For Polypropylene

The relationship among structure, properties and rheological behavior of impact polypropylene copolymer (IPC) has been thoroughly investigated. Based on the conclusions obtained during investigation, new polymer materials with excellent toughness-strength improvement have been manufactured. The main results of this thesis are described as follows:(ⅰ) Morphology evolution of the dispersed phase with the multilayered core-shell structure in IPC during molten-state annealing was systematically studied through scanning electron microscope, phase contrast microscope and dynamic rheological test. Different binary blends comprised of fractions were prepared and their diffusion behavior during liquid-liquid phase separation was investigated. The interaction parameters of these blends were investigated by using Nishi-Wang equation. Based on the diffusion rates, entanglement densities and viscosities of components, a potential mechanism was proposed for the morphology evolution of core-shell dispersed particles in IPC during molten-state annealing.(ⅱ) The influence of the dispersed phase on impact properties of IPC was systematically investigated by preparing a series of samples with different self-structure and size of dispersed particles. Results revealed that toughness of IPC at room temperature was determined by size and self-structure of dispersed phase, while toughness at low temperature seemed to be independent of core-shell structure of dispersed particle, and only dropped with the increase of rubber size.(ⅲ) Toughening with little rigidity loss was achieved by adding high density polyethylene (HDPE) into polypropylene/ethylene-propylene random copolymer (PP/EPR) blends to fabricate a series of PP/EPR/HDPE ternary blends with core-shell dispersed particles. Dynamic mechanical analysis results showed that the introduction of HDPE could increase glass transition temperature (Tg) and loss peak area of EPR in PP/EPR/HDPE blends, which is similar to the effect of adding EPR in PP/EPR. According to percolation of stress volumes, the interparticle distance was proposed to be a key factor of toughening effect of rubber particles in thermoplastic and thereby a toughening mechanism about the equivalent rubber content was established to explain balanced toughness-strength improvement of PP/EPR/HDPE blends with core-shell particles. The rubber particles with core-shell structure lead to the increase of particle size and the decrease of interparticle distance on the premise of not increasing actual rubber content, resulting in a notable improvement of toughness, while the ’hard’ core made from HDPE component provides a satisfied rigidity.(iv) By introducing polymer M into PP/EPR blend, the thermal stresse induced by mismatch of thermal expansion coefficients of components was increased, leading to much lower glass transition temperature of rubber domain. The brittle-tough transition then shifts towards lower temperature, resulting in the improvement of toughness at low temperature.(v) The rheological bevavior of PP/EPR and PP/EPR/HDPE blends was studied. It was proposed that core-shell particles contribute to maintaining the structure and properties of material under external pressure.