Study On Sturcture And Properties Of Polyphenylene Oxide/polyamide 6 Blends And Composites

Poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide (PPO/PA) blends are of great importance for fundamental research and application of engineering plastics. PPO and PA are complement in thermal stability, solvent resistence, water resistance, dimension stability and processibility. In addition, as engineering plastics, they all have good mechanical properties. So blending PPO and PA has chance to obtain the materials with high HDT, good dimension stability, good chemical resistance and good processibility. At present, as one of rapidly developing plastic blends, PPO/PA6 blends have beed widely used in many industries.In terms of the poor compatibility, the simply blending of PPO and PA is useless for application. Furthermore, for the needs of high performance, it is necessary to modify PPO/PA blends. In this dissertation, the compatibilization, toughening, reinforcement and functionalization of PPO/PA6 blends were systemically investigated. The relationships between structure and properties of PPO/PA6 blends were also studied in detail.Due to the discrepancy of the components on crystallinity and polarity, PPO/PA6 blends are kinds of typical incompatible blends with serious phase separation, poor bonding power of interface and poor mechanical properties. In this dissertation, styrene-maleic anhydride copolymer (SMA) and maleated PPO (PPO-g-MA) were used to compatibilize PPO/PA6 blends and led to the significant decrease of disperse phase size and the improvement of interface. Furthermore, PPO-g-MA show the higher efficiency of compatibilization than SMA for PPO/PA6 blends. The study of compatiblization mechanics showed that PPO-co-PA6 emulsified PPO in PA6. By SEM and rotational rheometer, the relationship between the phase structure and rheological behavior of PPO/PA6 blends were studied. By Bousmina model, the viscoelasticity of PPO/PA6 blends was studied.Because of the incompatibility and relatively low toughness of PPO and PA6, PPO/PA6 blends have low notched impact strength. Then some impact modifiers, usually elastomers, have been used to toughen PPO/PA6 blends. In this dissertation, PPO/PA6 blends were impact modified by addition of three kinds of maleated polystyrene-based copolymers, i.e., maleated styrene-ethylene-butylene-styrene copolymer (SEBS-g-MA), maleated methyl methacrylate-butadiene-styrene copolymer (MBS-g-MA), and maleated acrylonitrile-butadiene-styrene copolymer (ABS-g-MA). The selective location of the maleated copolymers in one phase or at interface accounted for the different toughening effects of the maleated copolymer, which is closely related to their molecular structure and composition. SEBS-g-MA was uniformly dispersed in PPO phase and greatly toughened PPO/PA6 blends even at low temperature. MBS-g-MA particles were mainly dispersed in the PA6 phases and around the PPO phase, resulting in a significant enhancement of the notched Izod impact strength of PPO/PA6 blends. In comparison, the ABS-g-MA was mainly dispersed in PA6 phase without much influencing the original mechanical properties of the PPO/PA6 matrix. The different molecule structure and selective location of the maleated copolymers in the blends were reflected by the change of rheological behavior as well. By Erying theory and Wu theory, the toughening mechanism of SEBS-g-MA on PPO/PA6 blends was analysised. By single-edge notched tensile test (SENT) and single-edge notched three-point bending test (SEN3PB), the fracture behavior of PPO/PA6/SEBS-g-MA blends were investigated in detail.PPO/PA6 blends were reactively compatibilized by PPO-g-MA and reinforced by short glass fiber (SGF) via melt extrusion. An observation of the SGF-polymer interface by scanning electronic microscope (SEM) together with etching techniques indicated that PPO-g-MA played a decisive role in the adhesion of polymers to SGF. The rheological behavior was investigated by capillary rheometer,and the addition of PPO-g-MA and SGF could largely increase the viscosity of the PPO/PA6 blends. The analysis of fiber orientation and distribution in the PPO/PA6/SGF composites showed PPO-g-MA favored to the random dispersion of SGF. The statistic analysis of SGF length showed that PPO-g-MA was helpful to maintain the fiber length during melt-processing. For the composites at a given SGF content of 30 wt%, the addition of PPO-g-MA increased the tensile strength from 59.4 MPa to 97.1 MPa and increased SGF efficiency factor from 0.028 to 0.132. By Kelly-Tyson model SGF reinforcement mechanism was explored. The fracture toughness of the composites was investigated by single edge notch three-point bending test.Organic-inorganic nanocomposites have drawn great attention due to their excel combination of properties of organic polymers and with inorganic systems. In this dissertation, PPO/PA6 (50/50) blends filled with epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) were prepared via melt mixing. The reaction between POSS and PPO/PA6 blends was studied by Fourier transform infrared spectroscopy, end group and gel content tests. The morphology of PPO/PA6/POSS composites was observed by field emission scanning electron microscope and transmission electron microscope. As a chain extender and a crosslinking agent for PA6, POSS largely affected the morphology of the composites, which was mainly dependent on the melt-viscosity ratio and interfacial tension between the components. With increasing POSS content from 2 to 4 phr, the morphology of the composites transformed from droplet/matrix to co-continuous morphology. The PPO/PA6/POSS composites with co-continuous morphology had the better mechanical properties than those with droplet/matrix morphology. The addition of POSS could improve the water resistence and thermal stability of PPO/PA6 blends. The different dispersion and reaction of nano-silica or surface modified nano-silica in the PPO/PA6 (50/50) matrix could lead to different change of morphology of the composites. The result of thermal gravimetry analysis implied that the addition of silica particles could significantly improve the the thermal stability of PPO/PA6 blends. In the PPO/PA6/mltiwalled carbon nanotubes (MWNTs) composites, most MWNTs were selectively dispersed in the PA6 phase. The electrical conductivity and conductive mechanisms of the PPO/PA6/MWNTs composites were largely related to the dispersion of MWNTs and the morphology of the composites. Comparaed with PPO/PA6 (80/20) blends filled with MWNTs and PPO/PA6/SMA (50/50/4) blends filled with MWNTS, PPO/PA6 (50/50) blends filled with MWNTs showed the lowest electrical resistivity and the lowest filler loading, which could be explained by a double percolation effect.The innovative points of this dissertation are listed as follows(1) The grafted location of MA on PPO chains was investigated by FTIR and NMR analysis. The change of morphology and rheological behavior of PPO/PA6 blends with the compatibilizers were quantatively anaylised.(2) A way to prepare the PPO/PA6 blends with super toughness (notched Izod impact strength above 900 J/m) was given. A way to improve the impact strength and processibility of PPO/PA6 blends was given. The mechanism of SEBS-g-MA toughening PPO/PA6 blends was quantitatively studied. The toughness parameter of PPO/PA6/SEBS-g-MA blends was characterized using SENT and SEN3PB method, which was helpful to the understanding of the toughening mechanism of the PPO/PA6 blends.(3) A way to improve the interfacial action of PPO/PA6/SGF composites was given. The mechanism of SGF reinforceing PPO/PA6 blends was quantitatively studied by Kelly-Tyson model.(4) A method of chain-extended and chain-crosslinked PA6 was investigated. The PPO/PA6 blends filled with POSS had better mechanical properties, better thermal stability and lower water absorption, which is an advantage for the storage, processing and application. The relationships between the morphology and the rheological behavior and the interfacial tension of PPO/PA6/POSS composites were quantitatively studied.(5) A method of surface modification of nano-silica was given. Nano-silica with this surface modification could compatibilize the PPO/PA6 blends and lead to better mechanical properties, solvent resistance and thermal stability. A way to prepare antistatic PPO/PA6 blends was given. The relationship between electrical conductivity and phase structure of PPO/PA6 blends was investigated.