Investigation On Blend Of Fully Vulcanized Polybutadiene Nanoparticles/Polypropylene By Compounding

Many researchers have focused on developing of commercial polymer materials with desired properties and multiple functions. In this study, a new kind of fully vulcanized nano-powder rubber was prepared by vacuum spray drying method from pre-irradiated polybutadiene rubber latex. Both PP/UFBR and PP/PP-g-MA/UFBR blends were prepared by solution method and melt compounding. The influences of the composition and ratio of the UFBR and maleic anhydride graft polypropylene (PP-g-MA) concentration on the crystallization properties, morphological properties, mechanical properties and rheological properties of the blends were systematically investigated. It is especially important, not only from a scientific point of view but also from an industrial point of view, to study the mechanism of toughening and percolation network structure formation for this new kind of PP/UFBR blends.Fully vulcanized polybutadiene nano-powder (UFBR) with nano-scale distribution was firstly prepared by vacuum spray drying technology from the corresponding polybutadiene rubber latex pre-irradiated byγ-ray from 60Co or E-beam from electron accelerator.The mechanism of radiation crosslinking by incorporation with and without unsaturation monomer has been evaluated, both the influence on microstructure and efficiency of unsaturation monomer on enhancement radiation vulcanization were investigated. It is the first time that the n-butyl methacrylate (n-BMA) was introduced and evaluated as unsaturation monomer in the polybutadiene latex, compared with that of n-butyl acrylate (n-BA) for enhancement radiation vulcanization. The results showed that n-BMA is superior to n-BA both in enhancement efficiency and sterical selectivity. The latex composition incorporating with optimum concentration of unsaturation monomer and irradiation processing condition were determined for the consequent upon practical latex pre-irradiation.The crosslinking kinetics of neat PBL, fitting very well with Charlesby–Pinner equation, is predominately random crosslinking. However, the enhancement system disagrees with Charlesby–Pinner equation and even further with increasing addition of monomer, which is predominately grafting mechanism. Gel fraction closely relates to irradiation dosage and less to irradiation dose rate. Fourier transform infrared (FTIR) spectroscopy demonstrated that the absorption intensities, due to C=C stretching, decreasing with increment of irradiation dosage, which attributes mainly to crosslinking, and the appearance of absorption peaks indicate the formation of carbonyl group and hydroxyl group respectively due to oxidation during irradiation. These results revealed the microstructure changes after irradiation and provided information of surface properties for UFBR particle.The atomic force microscopy (AFM) demonstrated that the UFBR particles observed with isolated spheroid approximately, have a significant difference in size diameter of 26~100 nm. This phenomenon suggests that the aggregation and permanent sticking together of particles can be effectively prevented by crosslinking, although a few aggregates can still be observed. It is a unique methodology for UFBR preparation from pre-irradiated latex.Dynamic mechanical analysis (DMA) was performed to investigate the effect of radiation vulcanization on dynamic storage modulus (E'), loss modulus (E") and damping (tanδ). The steady increase in storage modulus (E') and the shift of relaxation spectra to higher transition temperature with dose, and the transition temperature (Tg) increased from -75°C to -69°C, the E'from 4.161×106Pa to 5.314×106Pa,for un-irradiated PBL and PBL irradiated respectively, which all attributed to heavy crosslinking structure formation.Influence of neat PP, PP/UFBR and PP/PP-g-MA/UFBR blends on crystallization properties, morphological properties and mechanical properties were investigated. Differential scanning calorimetry (DSC) analysis demonstrated that the surface of UFBR particle had heterogeneous nucleation effect on PP crystallization, which leads crystallization temperature increased and melting temperature decreased on the addition of UFBR, since UFBR retards the crystal growth, which leads to unperfected crystals. Wide-angle X-ray scattering (WAXD) diffraction further stated that the addition of UFBR into PP increased the interplanar distance (d value) and decreased lateral sizes. This indicates that UFBR particles are present in the intra spherulitic structure of PP. UFBR is more likely for PP to crystallize into theβ–phase, and increment with increasing of UFBR concentration, since it retards the transition fromβ-phase toα-crystalline. As the surface of UFBR covered with PP-g-MA, its function in heterogeneous nucleation effect,β-phase inducing and lateral sizes reducing deteriorated. However, PP-g-MA can enhance interfacial interaction and adhesion, which resulted in even distribution of UFBR in PP matrix, and increment of interfacial area. The impact strength of PP/UFBR blends increased with increasing addition of UFBR, in maximum of 500%, however, the elongation at break decreased. Nevertheless, the elongation at break increased obviously, reaching 430.8% in PP/PP-g-MA/UFBR blends, for interfacial adhesion improvement. The SEM photography also indicated that fibrous material on the fracture surface of the PP/UFBR and PP/PP-g-MA/UFBR blends due to the yielding of the matrix ligaments between the particles and the matrix. This implied that brittle-ductile transition depends on both UFBR concentration and interfacial interaction.The dynamic rheological properties of PP/UFBR and PP/PP-g-MA/UFBR blends were investigated, and found that dynamic rheological behavior having sensitive responding with the composition of blends. The complex viscosity(η*) increased with increasing addition of UFBR, second plateau appeared in G'(ω) and tanδ(ω) curve exhibited a zero-slope plateau in the low frequency regime, all these known as the transition from pseudo-liquid-like to pseudo-solid-like, attributed to formation of network structure by UFBR particles. PP-g-MA can promote percolation network structure formation at lower UFBR critical concentration, for its enhancement interfacial interaction and adhesion.Influence of solution method and melting compounding on the distribution of UFBR particles were also investigated. The percolation network structure threshold is about 10 mass% for solution method with weak shear stress, which leading to even distribution of UFBR in PP matrix. However, the threshold increased to 20 mass % for melting compounding with strong shear stress, which resulted from aggregation of UFBR particles. Comparing with other nano-particles filled system, the decrement of threshold indicated that the distribution of UFBR particles was improved obviously.The rheological behaviors characterizing the long relaxation time mode were further enhanced with the increasing concentration of UFBR in PP/UFBR blends, as that of long branched chain polypropylene (LCBPP). The unusual shear rheological behaviors indicated that UFBR particles served as crosslinking points in view of the role of entanglement of chains as a long relaxation time mode within LCBPP. Enhancement of melt properties via the strain-hardening behavior during the extensional flow by taking account of retarding the movement of polymer chains. The strain-hardening behavior was further enhanced with addition of PP-g-MA, since interaction between UFBR particles and PP matrix improved greatly. A novel method might be explored for preparation of high melt strength polypropylene (HMSPP) by compounding.