Structure And Properties Of Polymer/inorganic-particle Nanocomposites

Carbon nanotubes (CNT), one of the most representative one-dimensional nanomaterials, are the ideal reinforcement additives for nanocomposites owing to their nanometer scale, unique and perfect microstructure, large aspect ratio, super high mechanical strength and good electrical conductivity. Therefore the synthesis and properties of CNT nanocomposites are one of the research hotspots in polymer science.Nylons have many excellent properties, and they have been widely used in many fields. The nylon used in this paper is just nylon1010 with ten methylenes in the main chains. Compared with some commercialized nylons, such as nylon 66 and nylon 6, they show some special properties including higher toughness, lower melting point, lower density and lower moisture absorption and so on. On the other hand, there is increasing interest in the nanocomposites of nylon and carbon nanotubes because of their excellent properties, such as good mechanical properties, high thermal stabilization, excellent electric properties and fireproof properties.Polypropylene (PP) is an important general plastic and has an important effect on the plastic industry because of its high ratio of performance/price. For enlarging the application of PP, the improving property of PP is one of important research aspect in the development of plastic industry. It is a new method to improve the property of PP with carbon nanotube. In virtue of excellent performance of carbon nanotube, a new functional nano-plastic will be obtained. Therefore, it is very theoretic important and has a broad application prospect to research this project.PA1010/CNT and PP/CNT nanocomposites are prepared by melt mixing in this paper and the performances of the nanocomposites are systemically studied, such like thermal stabilization, crystallization behavior, rheological property, dynamic mechanical property, electric property and morphological structure and so on.The introduction of CNT into PA1010 obviously improves the thermal stability of polymer matrix. Moreover, high MWNT loading has better effect on improving thermal stability while it is opposite for MWNT-COOH. This is correlative with the dispersion of CNT, good thermal conduction of CNT and hindering the diffusion of polymer decomposed product. The DSC results show that CNT accelerate the growth of PA1010 crystals as the nucleant seeds. Moreover, with increasing the CNT loading, the speed of crystallization enhanced and the distribution of crystal size decreased. Also, the crystallization temperature and speed of crystallization are more effectively improved for MWNT-COOH than MWNT at the same content of CNT. Rheological results show that the introduction of CNT has evidently effect on the complex viscosity, storage modulus and loss modulus, especially in the low frequency region. PA1010/MWNT nanocomposites show the pseudo-plastic liquid behavior and CNT slower the relaxation of PA1010 chains. Furthermore, PA1010/MWNT nanocomposites exhibit stronger shear-thinning behavior than pure PA1010. SEM results show that MWNT evenly disperse in the PA1010 matrix and closely contact with polymer matrix without hollow. Mechanical property tests show that the addition of CNT enhanced the tensile modulus of polymer matrix and depressed the elongation at break at the same time. Further, the effect of improvement mechanical property of MWNT-COOH is better than that of MWNT for the same CNT loading.Thermal gravimetric analyses (TGA) showed that carbon nanotubes significantly enhanced the thermal stability of polypropylene in nitrogen. The temperature of onset decomposition was higher than that of neat PP over 44oC for nanocomposites with 3wt% of MWNT loading. The effect of MWNT on the crystallization and melting behavior of polypropylene was not observed. Rheological behavior of PP/MWNT nanocomposites showed that storage modulus (G′) and loss modulus (G″) increased with increasing nanotube content. At low frequency, the steady shear viscosity of nanocomposites with 1wt% of MWNT loading was minimal and that of the sample with 5wt% nanotube was maximal. Shear thinning tendency increases with the increasing frequency. The volume resistivity and surface resistivity of nanocomposites with 5wt% MWNT were 9 and 4 order of magnitude, respectively lower than those of neat PP. This shows that the electrical conductivity can be improved obviously by incorporating a little MWNT.High pressure is a typically extreme physical condition which can effectively change the space among the atoms and the status of atomic lamellas. High pressure is a new method through which people can further understand the physical phenomena at atmosphere and discover the new phenomena, new rules and new materials that only arise under high pressure. High pressure has an obviously effect on the structure of polymer. Wunderlich early discovers that PE can crystallize into chain-extended crystal with molecular chains fully extended under 5000 atmosphere pressure. To compare with folded-chain crystal obtained at atmosphere pressure, the extended-chain crystal has high melt temperature, high modulus and strength. Extended-chain crystals are thermaldynamic most stable congregative structure of polymer. It is interesting to research the structure and morphologies of nylon under high pressure because it is a kind of universal engineering plastic with good performance. Gogolewski and Huang etc. have studied the mechanisms and growth conditions of extended-chain crystal of different nylons. The results show that nylon6, nylon66, nylon 11 and nylon12 all can obtain their extended-chain crystal under high-pressure crystallization. It is difficult to directly obtain extended-chain crystal of neat nylon and the introduction of the second element can make the extended-chain crystal grow under the more moderate condition. Thus, the melt crystallization behavior and annealing behavior of PA1010/CNT nanocomposites under high pressure are systemically investigated in this paper.The DSC results show that the melt temperature, melt heat enthalpy and crystallinity of PA1010/CNT composites melt crystallized under high pressure are all distinctly increased. For example, the maximum melt point and crystallinity are 209oC and 64.6%, respectively. It suggests that the extended-chain crystals with high melt point are obtained. Moreover, the multi-melt peaks and single peak are emerged in the melt heat curves and the sample will change into amorphous structure at the certain pressures. For the PA1010/CNT composites annealed under high pressure, the melt point, melt heat enthalpy and crystallinity etc. are comparative with that of neat PA1010. Higher pressure (larger supercooling) may freeze the motion of molecular chains and restrict the growth of crystal. Therefore, the effect on the growth of extended-chain crystal is very different for the melt crystallization and annealing under high pressure.The IR results show that a closer packing of the polymer chains occur in the PA1010/SWNT sample melt crystallized under high pressure. The occurrence of the free N-H groups in the pressure-induced crystallized PA1010/SWNT sample may be attributed to the break of the hydrogen bonds to some extent. X-ray results show that the intensity of (100) diffraction peaks for samples crystallized under high pressure are weaken than that for samples crystallized at atmosphere pressure, which attribute to the break of hydrogen bonds by high pressure. However, the intensity of (010) diffraction peaks held together by Van der Waals forces are obviously enhanced for the samples crystallized under high pressure. Further, a shifting of the peaks in the direction of higher angles and smaller spacing were observed.The SEM and TEM results vividly exhibit that the striated extended-chain crystals of PA1010/SWNT composites are obtained through melt crystallization under high pressure and the thickness along c-axis of the extended-chain crystals of PA1010/SWNT composite was beyond 150μm. The interpenetrating network structures between SWNT and PA1010 matrix can be observed from the failure surfaces of broken extended-chain crystals, implying that SWNT may be as seed nuclei for growth of extended-chain crystals under high pressure. Besides, some regular block-like crystals are also observed in the high-pressure crystallized samples. For PA1010/MWNT-COOH composites, the spherulites and rod-like crystals are observed besides the striated extended-chain crystals. Moreover, the morphological structure of MWNT-COOH under high pressure has changed which show a grain-like structure and a larger diameter, implying that the surfaces of MWNT-COOH are covered with a layer of polymer matrix.The extended-chain crystals of PA1010/CNT composites can be obtained both through melt crystallization and annealing under high pressure. Furthermore, melt crystallization under high pressure is a more effective method on the promoting growth of extended-chain crystals of PA1010/CNT composites. Three mechanisms (transamidation, SWNT nucleation, and chain-sliding diffusion) may work together to promote the rapid thickening of the crystal in PA1010/SWNT composites and finally lead to the growth of the large extended-chain crystal. The research on the polymer/montmorillonite nanocomposites has stimulated huge interest since the nylon6/montmorillonite composites prepared by melt intercalated method was reported by the center institute of Toyota in 1987, because of its excellent various properties than neat nylon6. Many researches indicate that polymer/montmorillonite nanocomposites with loading lower than 10wt% have high strength, high modulus, good thermal stabilization, good isolation, good transparence and fireproof property.Polylactic acid (PLA), a kind of synthetical aliphatic polyesters, bears wonderful biologic compatibility and biodegradable property, which is harmless and non-toxic to the environment as it can finally biodegrade into CO2 and H2O. Its raw material resource is lactic acid obtained from starch with fermentation. It has been used as one of the most important biomedical materials. At the same time, with physical mechanical properties similar to popular plastics, PLA can substitute for them. Polylactic acid will become an industrial material with considerable perspective. However, PLA is easy to decompose and hydrolyze at high temperature. The melt viscosity of PLA is not very sensitive and the melt has relatively poor strength. So, the processing conditions of PLA are very rigorous. Thus, to enhance the rheological properties of PLA for operations where shear sensitivity and/or melt strength are desirable, incorporating the organically modified montmorillonite is employed in view of the much predominant properties.Polylactide/organically modified montmorillonite nanocomposites (PLA/OMMT) have been successfully prepared by melt-compouding technique in this paper. The rheological behavior, dynamic mechanical behavior and morphological structure of composites are systemically investigated. Also, some light stabilizers and antioxidant are employed to improve the thermal stability of PLA matrix.The rheological behavior of nanocomposites showed dependence of both temperature and OMMT content. For the polymer and the nanocomposite of low OMMT content, the complex viscosities show a Newton plateau in low frequencies at low temperatures. The nanocomposites exhibit strong shear-thinning behavior and non-terminal viscoelastic behavior at high temperature or high loadings of layered silicate. The dependence of relaxation behavior on the temperature for PLA/OMMT nanocomposites is very different from that of pure PLA, which attribute to the confinement effect of two-dimensional anisotropic layered silicate. Time sweep tests show that addition of 5wt% OMMT remarkably enhances the stability of PLA matrix.WAXD and TEM show the exfoliated nanocomposites form at low OMMT concentrations and a mixture of exfoliated and intercalated nanocomposites is obtained at high OMMT loadings. TGA shows that thermal stability of the nanocomposites is slightly improved by introduction of 5wt% OMMT. However, the stability significantly decreases at higher OMMT content which is probably owing to relatively poor OMMT dispersion. DMA shows that the storage modulus and glass transition temperatures of PLA/OMMT composites gradually increase with increasing OMMT content.