Preparation Of Polymer/Rubber Praticles/Carbon Nanotubes Composites And Their Structure And Properties

Carbon nanotubes(CNTs) have been considered as an ideal mulfunctional nanofillers due to their special geometric structure in combination with superior electrical properties and mechanical properties, which can be used for preparation of high performance polymer composites. In particular, antistatic or conductive composites of CNTs/insulating polymers have important application prospect. To reduce the percolation threshold of polymer/CNTs composites, a method which is simple and suitable for large-scale application has been developed, i.e., a kind of ultra-fine rubber particles (URP)is introduced to the matrix as the third component. URP could change the dispersion, distribution and stretching state of CNTs and prepare polymer/URP/CNTs ternary composites with low percolation threshold. Moreover, URP could enable polymers to have high-performance applications. In this thesis, the relationships between microstructure and properties of differernt polymer/URP/multi-walled carbon nanotubes(MWCNTs) ternary composites have been systematically investigated. Firstly, CSRP/MWCNTs compound powder with surface-loaded structure was prepared and CSRP acted as carriers of MWCNTs. URP could be well dispersed in PA6 matrix because of its special microstructure. With the help of URP, on the one hand, MWCNTs could be well dispersed in PA6 and form conducting pathway; on the other hand, MWCNTs could be stretched in random directions and consequently increased effective aspect ratio to form more effective conducting pathway. As a result, PA6/CSRP/MWCNTs composites with low percolation threshold have been prepared. The mechanism on better dispersion and stretch of MWCNTs with the help of URP was also given. With the addition of 16 phr URP, the percolation threshold of PA6/MWCNTs composites was reduced from 6 phr MWCNTs to 3phr. Besides, at a constant loading of 4 phr MWCNTs, increase of URP loading led to two changes and a plateau for the volume resistivity of composites. The rheology resulted confirmed that CSRP had interaction with URP. The complex viscosity and storage modulus at lower frequencies of PA6/CSRP/MWCNTs composites significantly incerased compared that of PA6/CSRP and PA6/MWCNTs composites. Dynamic mechanical analysis showed the addition of MWCNTs increased storage modulus of PA6/CSRP composites throughout the temperature range; TGA data show that the introduction of CSRP/MWCNTs did not affect the initial decomposition temperature of PA6; Crystal data show that PA6/CSRP/MWCNTs mainly contained a-crystallites. Secondly, electrically conductive thermoplastic vulcanizates (TPVs) filled by MWCNTs are prepared by a simple one-step melt mixing process, based on linear low density polyethylene (LLDPE) and URP. URPs were dispersed in LLDPE with micron-scale particle size and mainly palyed a role of volume exclusion. As a result, the effective concentration of MWCNTs in LLDPE increased and conducting pathway was formed. On the one hand, the structure and properties of LLDPE/SBRP-70/MWCNTs were carefully studied. The as-prepared TPVs showed typical two-phase structure with URP as dispersed phase. MWCNTs were selectively distributed in LLDPE matrix. By controlling the LLDPE/SBRP-70 blend ratio, a series of electrically conductive TPVs with different volume resistivity and mechanical properties could be obtained. On the other hand, MWCNTs/TPVs with different URP(SBRP-70, SBRP-50, NBRP) was investigated. For LLDPE/NBRP system, MWCNTs were not only distributed in LLDPE, but also tended to be distributed in the interface of LLDPE and polar NBRP. Therefore, LLDPE/NBRP system showed the lowest percolation threshold. For LLDPE/SBRP system, the polarity of the two phase was similar, then MWCNTs tended to be distributed in the low viscous LLDPE matrix. Compared to SBRP-50, SBRP-70 had better compatibility with LLDPE and showed better dispersion. As a result, SBRP-70/LLDPE system had lower percolation threshold and better mechanical properties. It is found that CSRP with low Tg could increase the Tg of polyamide with high Tg in polyamide/CSRP partially compatible system. The phenomenon was in contrast with the traditional theory, which stated that the two Tgs of partially compatible composites should be close to each other. A possible explanation has been proposed. CSRP could be well dispersed in polyamide with diameter 150 nm, therefore there existed large phase interface between CSRP and polyamide. The movement of polyamide molecular chain was restricted in the phase interface and hence Tg of polyamide increased.