Preparation Of Carbon Nanotubes/Liquid Crystalline Polymer Composites And Their Influence On Crystallization Behavior Of PP

In recent year, it has been a major way to develop new high performance polymer materials through modifying polymer, which has attracted more and more attention. Carbon nanotubes (CNTs) not only have excellent mechanical properties, chemical and thermal stabilities, and electrical conductivity, but also have length-diameter ratio greater than1000, which make CNTs being a perfect reinforcement agent for polymer composites, and can give many new functions. Liquid crystalline polymers (LCPs) have some advantages, such as high orientational order, modulus and strength, and had been applied in thermoplastic blends as a new polymer adjuvant. LCPs exist in polymer composites in the form of micro-fibre, and can be used as compatibilizer. In the dissertation, the CNTs/LCPs composites were prepared by solution mixing and in situ polymerization.Firstly, the multiwalled carbon nanotubes (MCNTs) were purified to achieve a large number of active groups on MCNTs with mixed acid acidification or chlorine oxidation. Liquid-phase oxidation was used in the mixed acid purification. However, from the point view of practical application, the chlorine purification with the merits of gas-phase oxidation, liquid-phase oxidation and acid treatment, was easily carried out to satisfy the need of massively purifying MCNTs in industry. FT-IR spectrum showed that the hydroxyl and carboxyl groups on the surface of MCNTs were obtained by oxidation. Sedimentation experimental results showed that the purified MCNTs could be easily dispersed in polar solvents. Wide angle X-ray diffraction (WAXD) indicated that the crystal structure of the purified MCNTs did not change and the degree of crystallization increased. It was also shown that catalyst particles, amorphous carbon and carbon particles were almost eliminated after purification. Scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) indicated that more hydroxyl and carboxyl groups on the MCNTs were obtained by chlorine purification because of its stronger oxidizing, but the dispersion effect should be further improved.Secondly, two new nematic monomers were synthesized, which including4-(undec-10-enoyloxy)biphenyl-4’-ethoxybenzoate (M1),4-(4-(2-(acryloyloxy)ethoxy)-benzoyloxy)phenyl-4’-ethylbenzoate (M2). The polymer P1was prepared by graft polymerization reaction with M1and PMHS. The polymer P2was prepared by free radical polymerization reaction with M2. The chemical structures and mesomorphism of these monomers and polymers were characterized by FT-IR, polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). FT-IR spectrum showed that the structures of the monomers and polymers were confirmed. M1and M1were thermotropic liquid crystalline compounds. M1exhibited enantiotropic nematic threaded textures and monotropic mosaic texture of smectic B (SB) phase, schlieren texture of smectic C (Sc) phase and fan-shaped texture of smectic A (SA) phase, on cooling process. M2exhibited typical nematic threaded texture on heating and cooling cycles. The polymers P1and P2showed nematic phase. DSC curves of P1showed a melting transition and nematic to isotropic transition, while P1showed a glass transition and nematic to isotropic transition. TGA showed that the temperatures at which5%weight loss occurred (Td) were greater than370℃for P1and P2, this indicates that these two polymers had a good thermal stability.Thirdly, MCNTs/LCPs composites (s-P and o-P) were prepared by solution blend and in situ polymerization, respectively. The chemical structure, phase behavior and mesomorphism of s-P and o-P were investigated with FT-IR, DSC, SEM and POM. The MCNTs in LCPs did not change the chemical structure of LCPs matrix, but they can improve the melting temperature (Tm) or glass transition temperature (Tg), clearing temperature (Ti), and the mesophase temperature range of s-P and o-P. In addition, the MCNTs in LCPs did not obviously affect the texture and mesophase type, but affected the mesophase transition temperature. SEM and POM showed that a small quantity of MCNTs was well dispersed in the LCP matrix and made the mesophase more stable. Fluorescence results showed that there was effective energy transfer and conjugate effect between MCNTs and the LCP matrix.Fourthly, the blends o-P1-3/PP and o-P2-3/PP containing different mass fraction of o-P1-3or o-P2-3were prepared by melting mixing at proper technical condition. The influence of o-P1-3and o-P2-3on the crystallization structure, morphology, thermodynamics, and kinetics and of blends was discussed with WAXD, DSC and SEM. The experimental results showed that MCNTs/LCPs composites with low concentration in PP played a role in the heterogeneous nucleation effect, enhanced the crystallization velocity and temperature. Moreover, β-phase was induced in PP. SEM indicated that o-P1-3/PP blends had good surface compatibility.