Studies On Structures And Properties Of VERSIFY Copolymers And PP/VERSIFY Blends

VERSIFY Plastomers and Elastomers are the novel propylene-ethylene copolymers with an unique molecular architecture. The effect of ethylene comonomer content on the crystallization, mechanical and viscoelastic properties of VERSIFY copolymers was studied by DSC, DMTA, POM and WAXD. The introduction of ethylene-unit obviously changed the chain structure and crystallization structure of VERSIFY copolymers. The effect of VERSIFY copolymers on the crystallization behaviors of PP as well as the degradation behaviors of VERSIFY copolymers in the melt state induced through high intensity ultrasonic wave were investigated. The feasible ultrasonic degradation mechanism was proposed based on the viscoelastic characteristic of polymer melt, the effect of ultrasound on rheological behavior, morphology and property of PP/VERSIFY blends were studies. The main results are as follows:1. The crystallization behaviors, mechanical and viscoelastic properties of VERSIFY copolymers with different comonomer content and molecular weight were investigated. The introduction of ethylene comonomer changes the sequence length of crystallizable units and destroys the regular structures of PP chains, results in broadening the melting range of VERSIFY copolymers. The melting point, crystallization temperature and the overall crystallinity of VERSIFY copolymers decrease with the increase in the ethylene comonomer content. The thermal behavior and structure of VERSIFY copolymers isothermally crystallized at different temperature were studied. All samples exhibit multiple melting peak behavior, as well as melting over a broad temperature range. With increasing crystallization temperature, the spherulites size of VERSIFY copolymers increase and the numbers of nucleation decrease. The increase of crystallization temperature is favorable to the formation ofγ-phase for VERSIFY copolymers. At a fixed crystallization temperature the relative content ofγ-phase increases with increasing the ethylene comonomer content.2. The results of dynamic mechanical properties show that with increasing the ethylene comonomer content, both the stiffness and glass transition temperature of VERSIFY decreased. The dynamic rheological properties of VERSIFY copolymers were also investigated. The results showed that the increase of the ethylene comonomer content improved the plateau modulus (G_N⁰) and zero shear viscosity of VERSIFY copolymers, which is the cause that the introduction of the ethylene comonomer increased the entanglement density (v_e) of molecular chains for VERSIFY.3. The crystallization behaviors of PP/VERSIFY blends were investigated by DSC and WAXD. The addition of VERSIFY copolymers will decrease the crystallization temperature and broaden the melting range of PP. VERSIFY copolymers have no obvious influence on the melting point of PP. With the increase of the ethylene comonomer content and the decrease of molecular weight, the effect of VERSIFY copolymers on the crystallization and melting behaviors of PP is weakened. The influence of VERSIFY on nucleation rate constant (Kg) and fold surface energy (<σ_e) was examined by the nucleation theory of Hoffman and Lauritzen. The results show that both Kg andσ_e of PP/VERSIFY blends are slightly higher than that of PP, demonstrates that the overall crystallization rate of PP/VERSIFY blends decreased as compared to that of PP, owning to the decrease of the nucleation rate and the growth rate of PP. The isothermal crystallization kinetics of PP/VERSIFY blends were studied through polarizing optical microscope (POM). The results show that the growth rate of spherulites is decreased with increasing crystallization temperature for both PP and PP/VERSIFY blends. The growth rate of PP/VERSIFY blends is lower than that for PP at a fixed crystallization temperature. It was found that the higher the ethylene comonomer content, the worse the miscibility and interaction between VERSIFY and PP, the less the effect of VERSIFY on the growth rate of spherulites for PP. At the same crystallization temperature, with the preferred ethylene-unit content of VERSIFY copolymers, the growth rate of PP/VERSIFY blends is increased and closer to that of PP. The results show that the better the miscibility between PP and VERSIFY copolymers, the lower the growth rate of spherulite for PP/VERSIFY blends.4. The miscibility, morphology and mechanical properties of PP/VERSIFY blends were investigated. The addition of VERSIFY elastomers will decrease the tensile strength and Young's modulus, and improved the elongation at break of PP. SEM and AFM analysis show that PP/DP2000 (80/20) blends exhibits a homogeneous morphology, suggesting that DP2000 is miscible with PP because of low ethylene comonomer content. Whereas, PP/DE2300 (80/20) and PP/DE2400 (80/20) blends show the phase-separated morphology, the size of the disperse phase is at most 0.1 um, indicating that DE2300 and DE2400 are partial miscible with PP because of their high ethylene-unit content. The addition of DP2000 could not effectively improve the impact strength of PP whereas the addition of VERSIFY elastomers with high ethylene-unit content could obviously increase the impact strength of PP.5. The degradation behaviors of VERSIFY elastomers in the melt state induced through high intensity ultrasonic wave were investigated. The results show that the intrinsic viscosity [η] of VERSIFY elastomers significantly decreases with irradiation time in the first 100 s, and trends toward a limiting value for all samples. The ultrasonic degradation kinetics of VERSIFY elastomers in melt state follows the equation: M_t =M_∞+(M₀-M_∞]e^kt or [η]_t=[η]_∞+([η]₀-[η]_∞)e^kt The degradation rates are increased with the increase in ultrasonic intensity and the decrease in reaction temperature. The molecular weight is decreased and molecular weight distribution is broadened with increasing irradiation time, indicating that the chain scission is random for VERSIFY copolymers with narrow molecular weight distribution under ultrasound vibration. FTIR analysis showed that the degradation of DE2300 melt is caused due to the chain scission of propylene segments.6. Ultrasonic vibration can obviously decrease the die pressure and apparent viscosity of PP and PP/VERSIFY blends during extrusion. With the increase of ultrasonic power, the die pressure and the apparent viscosity of PP/VERSIFY blends will be further decreased. When ultrasound wave was introduced during extrusion, with the help of powerful vibration is well dispersed VERSIFY in PP matrix, the particles size of VERSIFY phase is reduced through ultrasound vibration. The impact strength and the elongation at break of PP/VERSIFY blends are improved. The physical and chemical effect of ultrasonic vibration on viscosity reduction of PP during extrusion was quantitatively examined. The results show that ultrasonic degradation is not the main cause of the reduction of apparent viscosity during extrusion in the presence of ultrasonic vibration.