Ultrasound Induced Development Of Structure And Properties Of Propylene Based Plastomer And Its Blends

By means of a static ultrasonic degradation device and an ultrasonic oscillations extrusion system developed in our laboratory, a novel propylene based plastomer (abbreviation: DP) and its blends/composites were studied systematically. The detailed experimental programs are as follows:1. Through a static ultrasonic degradation device, the effects of ultrasonic time, melt temperature, ultrasonic intensity and sampling location on the intrinsic viscosity, relative molecular weight and its distribution of DP as well as the ultrasonic degradation effect on the rheological behavior, melting, crystallization and mechanical properties of DP were studied.2. The effects of ultrasound on the die pressure, productivity of extrusion, melt apparent viscosity, melt surface appearance and die swell of propylene based plastomer were studied in the ultrasonic oscillations extrusion system where ultrasound was introduced into the die of single-screw extruder. The effects of ultrasonic degradation on tensile and dynamic mechanical properties of extrudates were also studied.3. Grafting of maleic anhydride onto DP was conducted during ultrasonic extrusion processing in the peroxide free conditions. The effects of ultrasonic intensity, die temperature and maleic anhydride content on grafting degree and efficiency and degradation were studied and their mechanisms were also proposed. In addition, some properties of PA6/DP-g-MAH 85/15 blends were investigated. 4. POE/DP blends with various concentrations were prepared in the presence of high-power ultrasonic oscillations during extrusion. The effects of components ratio and ultrasound on theology, phase morphology, mechanical and thermal properties of the blends were investigated.5. By the aid of high-power ultrasound, DP/nano-SiO₂ composites were prepared by means of melt blending. The effects of ultrasonic oscillations, surface modification and concentration of nano-SiO₂ on rheology, morphological, mechanical and thermal properties of composites were investigated. The experimental results respectively show:1. DP melt with higher melt viscosity near the ultrasonic probe tip readily degrades whereas the degradation of DP melt with lower melt viscosity behaves slightly. The relative molecular weight and intrinsic viscosity of DP decrease with the increase of ultrasonic time and they approach to a limiting value, along with the increase and following levelling off of relative molecular weight distribution of DP. The random rupture of macro-chain of DP melt is mainly concentrated on the portion of high relative molecular weight and propylene chain segment. It should be responsible for the the ultrasonic degradation that the melt, unable to relax between successive ultrasound, experiences a stepwise increasing stress. In addition, decreasing melt temperature and distance from probe tip and increasing ultrasonic intensity lead to an increase in the degradation of DP melt. In our experimental range, the effective distance of ultrasonic degradation is ca. 4 mm from the probe tip. The ultrasonic degradation behaviour of DP melt is also proved by the rheological experiment. Introduction of ultrasound decreases the various viscosities, viscoelastic moduli, cross modulus, relaxation time and the slope of log G'-logG" for DP melt, whereas the cross frequency and Dow rheological index get increased due to ultrasonic degradation. The chain segments with low relative molecular weight induced by ultrasonic degradation can crystallize at higher temperature due to their enhanced mobility and polarity. And, ultrasonic degradation can lead to a reduction in yield strength and deformation plateau of high elasticity. Compared with isotactic polypropylene, DP has a lower melting point, crystallization temperature, crystallization enthalpy and crystallinity as well as a broader melting distribution and smaller spherulite size. With ethylene content increasing, the crystallinity of DP further decreases. As a result, the yield strength of DP decreases but elongation at break increases, along with the occurrence of deformation plateau of high elasticity, compared with isotactic polypropylene.2. The presence of ultrasonic oscillations during extrusion can reduce die pressure and apparent viscosity, and increase the productivity of DP extrusion at the same die pressure. Introduction of ultrasound can reduce the dependence of DP melt on shear stress (rate) and process temperature, and inhibit die swell and melt fracture such as sharkskin. Higher ultrasonic intensity is more effective on the improvement of processability of DP with higher viscosity. Ultrasound-assisted extrusion can decrease the glass transition temperature (T_g) and storage modulus of DP due to the minor reduction in relative molecular weight, but show no significant impact on yield strength and strength at break as well as high-pressure capillary rheological behavior.3. With ultrasonic intensity increasing, grafting degree and efficiency of DP-g-MAH increase. In the presence of higher ultrasonic intensity, the lower die temperature is beneficial in the increase of grafting degree and efficiency. The increase of maleic anhydride content can elevate the grafting degree but reduce the grafting efficiency. MFI value of pure DP hardly changes under ultrasonic intensity of 200W. Without ultrasound, MFI value obviously increases in the presence of maleic anhydride and introduction of ultrasound can further elevate the MFI value. The phenomena can be proved by dynamical rheological and GPC data. The structure of DP-g-MAH initiated by ultrasound may appear as polymaleic and succinic anhydride units. Its blends with 85% PA6 show the smaller dispersed phase size and narrower size distribution compared with DP/PA6 15/85 blends. Complex viscosity and viscoelastic moduli also get increased. The phenomena are more obvious with grafting degree of DP-g-MAH increasing. In addition, DP-g-MAH has some influences on perfection of crystallite size of PA6.4. Both ulstrasonic oscillations and the addition of DP have a synergetic improvement on the processability of POE, including die pressure, apparent viscosity and productivity of extrusion. Viscosity values for the blends derived experimentally from high-pressure capillary rheological studies are slightly higher than those calculated theoretically using the log additivity principle, indicating the occurrence of partial compatibility between POE and DP in the melt state. With DP content increasing, yield point of the blends occurs and yield strength and strength at break gradually increase, indicating the gradual transition from elastomeric to plastic properties as a result of the phase invertion and elevation on the crystallinity of the blends as DP is added. The experimental data for elongation at break of the blends also display a positive deviation from additivity. Introduction of ultrasound can improve mechanical properties of the blends. In addition, the POE dispersed phase size gets decreased in the presence of ultrasound, along with the elevation of interfacial thickness and reduction of interfacial tension. FTIR and GPC data show that synthesizing of POE-DP copolymers in the presence of ultrasound can realize in-situ compatibilization to the POE/DP blends. DSC analysis shows that there is nearly no change of the melting temperature of POE and DP phases with the composition in blends. The presence of POE leads to nucleation effect during the crystallization of the DP. It is also verified that the POE phase can be prevented from crystallizing with increasing DP content in the blends.5. The lower nano-SiO₂ content (≤2wt %) can increase strength at break of DP but strength at break further decreases with increasing nano-SiO₂ content. Surface modification of nano-SiO₂ can improve elongation at break of composites. Introduction of ultrasound improves strength at break and elongation at break of composites, especially in higher nano-SiO₂ content (＞2wt %), and is beneficial in facilitating nano-SiO₂ dispersed in DP matrix. Dynamical rheological analysis shows that ultrasonic oscillations, surface modification of nano-SiO₂ as well as its decreasing content lead to the reduction of complex viscosity and viscoelastic moduli and elevation of the slope of logG'-logG" of composites. In addition, the critical value of strain where Payne effect occurs increases with the decrease of nano-SiO₂ content and its surface modification. Thermal analysis shows that the addition of nano-SiO₂ leads to increase of storage modulus of DP but decrease of loss modulus, T_g and tanδvalues of DP. Simultaneously, crystallization temperature increases but crystallization enthalpy decreases in the presence of nano-SiO₂. Loss modulus and tanδvalue of the composites increase whereas storage modulus and T_g of the composites decrease with the introduction of ultrasound, along with the further increase in crystallization temperature and decrease of crystallization enthalpy. In addition, ultrasonic degradation deteriorates thermal stability of the composites.