Study Of Pre-Irradiated Polypropylene And Syndiotactic 1,2-Polybutadiene Blends

Polypropylene (PP) is a widely used general propose thermoplastic. Though PP possesses many excellent properties, obvious drawbacks, such as poor impact strength, limits its applications. To promote practical properties and widen application areas, various approaches have been taken to modify the materials, and those extensive researches are highlighted in modifying thermoplastics worldwide. In this thesis, pp power was irradiated by low dose electron beam at ambient in air, then melt blended with syndiotactic 1,2-polybutadiene (s-1,2 PB), forming a pre-irradiated PP/s-1,2 PB blend which is compatibilized with in situ yielded PP-g-s-1,2 PB graft copolymer. In comparison of PP/s-1,2 PB blend without pre-irradiation, phase structure, mechanical properties, thermal properties and rheological behaviors of the blend systems were examined. The experiments provide valuable and systematic dada for developing high impact and/or high melt strength PP materials premising in wide practical applications.Characterized morphology of PP/s-1,2 PB blends and pre-irradiated PP/s-1,2 PB blends were isolated by SEM. The results showed that the s-1,2 PB particles dispersed as domains in PP continuous matrix, with the diameter of particle size less than 0.5μm when the content of s-1,2 PB was 10mass%. Both s-1,2 PB and PP phases existed as co-continuous phases when the s-1,2 PB content was more than 30mass% in the blends. Compatibility were improved obviously for pre-irradiated PP/s-1,2 PB blends compared with that of preserve PP/s-1,2 PB blends, which might be attributed to the interfacial reactions between components.The results of mechanical properties showed that the effect of irradiation dose for pre-irradiated PP with 1kGy on tensile strength is not so significant as that of the variation content of s-1,2 PB. The impact strength increased with increasing content of s-1,2 PB at room temperature, while no obvious improvement occurred for the blends at low temperature. The elongation at break for the blends of 1kGy pre-irradiated PP/s-1,2 PB was higher than that of PP/s-1,2 PB blends. The above results indicated that the interfacial adhesion between the PP and s-1,2 PB was enhanced after the pre-irradiation treatment.Differential scanning calorimetry (DSC) was used to characterize the thermal property, isothermal and nonisothermal crystallization kinetics of the blends of pure PP or pre-irradiated PP and s-1,2 PB. The results showed that incorporation of s-1,2 PB influenced the crystallization of PP matrix dramatically, while variation of irradiation dose had less effects to fusion and crystallization of PP of pre-irradiated PP/s-1,2 PB(90/10) blends. The investigation of isothermal crystallization kinetics showed that the s-1,2 PB acted as a heterogeneous nucleation agent and accelerated the crystallization rate, and the isothermal crystallization kinetics of the blends followed a three-dimensional growth via heterogeneous nucleation during the isothermal crystallization of the blends. The investigation of nonisothermal crystallization kinetics showed that it is suitable that the treatment by the Mo equation was appropriately employed to describe the nonisothermal crystallization process, but the Ozawa equation has a blemish for pure PP, 1kGy pre-irradiated PP and the blends. The Jeziorny equation had limitations to describe the nonisothermal crystallization process of pure PP and 1kGy pre-irradiated PP, but it is successful for the two blends too. The s-1,2 PB had a function of accelerating the crystallization. Both nucleation and growth rate of crystallization were changed after incorporation of s-1,2 PB, and the activation energy of isothermal and nonisothermal crystallization for the two blends were lower than that of pure PP and 1kGy pre-irradiated PP according to the Arrhenius and the Kissinger method, which revealed that s-1,2 PB acted as a heterogeneous nucleating agent during the crystallization of the PP in the two blends and accelerated the crystallization rate.The dynamic rheological behaviors of PP/s-1,2 PB and pre-irradiated PP/s-1,2 PB blends were investigated. The results showed that both two blends remain linear viscoelastic properties within the strain amplitude less than 10%. The phenomenon of shear-thinning appeared less obvious with increment of s-1,2 PB content in the large strain amplitude. The temperature and sweep of time effected storage modulus (G') dramatically, which resulted in structural changes of blends within linear viscoelastic region especially at higher temperature. Frequency scan demonstrated that the relaxation time of PP/s-1,2 PB blends increased with the increment of s-1,2 PB content at the region of low frequency, while the decrement of complex viscosities,η*, for blends at high frequency region implied the processability improvement of PP after incorporation of s-1,2 PB.Investigation of non-linear viscoelasticity for the different blends showed that these blends all demonstrated the characteristic of Newton fluids at low shear rate, while the shear stress and shear viscosity for the blends changed obviously after incorporation of s-1,2 PB. The investigation of rheological properties revealed that graft reaction initiated by pre-irradiated PP with s-1,2 PB might improve melt strength of the PP matrix.