Summary: Nanocomposite materials were obtained by blending multi‐wall carbon nanotubes (CN), obtained by acetylene catalytic chemical vapour deposition (CVD) on Co/Fe‐modified NaY zeolite, with syndiotactic poly(propylene) (sPP). The nanotubes, well dispersed in the polymer matrix, favour the crystallization of the sPP helical chains and significantly improve the sPP thermal stability either in nitrogen or in air. The morphology of the sPP affects the behaviour of the sPP degradation in air.
Thermogravimetric analysis in air of pure sPP and the nanocomposite material. 相似文献
Nanohybrid shish?Ckebab (NHSK), induced by polyamide 66 (PA66) nanofiber, was successfully fabricated in high-density polyethylene (HDPE)/xylene solution via isothermal crystallization. The crystalline morphological features of NHSK were observed by scanning electron microscopy. In the structure of NHSK, PA66 nanofiber serves as shish and HDPE lamellae act as kebabs periodically surrounding the nanofiber. Additionally, it reveals that both HDPE solution concentration and crystallization time have significant effects on the size of HDPE kebab. That is, as the concentration and crystallization time increase, the diameter of the kebab increases. Moreover, when crystallization time further increases, the crystals decorated on PA66 nanofiber exhibit a three-dimensional growth (i.e., aggregate of crystallites) rather than a two-dimensional one (i.e., disk-like lamellae normal to the axis of nanofiber). 相似文献
Crystallization analysis fractionation (CRYSTAF) has been introduced for the analysis of the composition of polyolefin blends and the chemical composition distribution of polyolefins. Blends of syndiotactic and isotactic polypropylene (sPP and iPP) and of sPP/High density polyethylene (HDPE) have been fractionated by CRYSTAF and the results been compared to those from DSC. While the blends of sPP and HDPE cannot be separated by DSC a quantitative determination of both components is possible by CRYSTAF over the whole range with the detection limit being 1% on both ends. Furthermore it is demonstrated that the separation of ternary blends of sPP, iPP and HDPE is possible by CRYSTAF. 相似文献
Crystallization kinetics of syndiotactic polypropylene(sPP)was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering.Initial time and growth time of crystallization were obtained,and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated. 相似文献
In this study, non-isothermal crystallization of neat high density polyethylene (HDPE) and HDPE/titanium dioxide (TiO2) composite was studied using differential scanning calorimetry. Non-isothermal kinetic parameters were determined by Jeziorny approach and Mo’s method. Polarized optical microscopy and wide angle X-ray diffraction were applied to observe the crystal morphology and investigate the crystal structure, respectively. It was found TiO2 particles could act as nucleating agent during the crystallization process and accelerate the crystallization rate. The Avrami index indicated nucleating type and growth of spherulite of HDPE was relatively simple. The result of activation energy indicated it was more and more difficult for the polymer chains to crystallize into the crystal lattice as the crystallization progressed. HDPE/TiO2 composites exhibited lower ΔE values, suggesting TiO2 particle could make the crystallization of HDPE easier. HDPE/TiO2 composites had much smaller spherulite size than that of neat HDPE. HDPE formed more perfect crystal when TiO2 particles were added into its matrix without changing the original crystal structure of HDPE. 相似文献
Summary: Various crystalline textures have been identified in a crystallizable block copolymer system, polystyrene‐block‐[syndiotactic poly(propylene)] (PS‐sPP), having a glass‐transition temperature of PS (Tg,PS) located in the midst of the sPP crystallization window. A confined morphology for the crystallization of sPP was observed while the crystallization temperature of sPP (Tc,sPP) was less than Tg,PS. A further increase in Tc,sPP could lead to a breakout in nanostructure. This study revealed the Tg effect on crystallization‐induced morphological changes of block copolymers from confinement to breakout.
TEM images and one‐dimensional SAXS profiles of PS‐sPP isothermally crystallized at TODT > Tg,PS > Tc,sPP (top) and TODT > Tc,sPP > Tg,PS (bottom). 相似文献
Non-isothermal melt-crystallization and subsequent melting behavior for six syndiotactic polypropylene (sPP) resins having different molecular characteristics were investigated by differential scanning calorimetry (DSC). For a given sPP resin, the crystallization exotherm became wider and shifted towards a lower temperature with increasing cooling rate. Among all of the sPP resins investigated, the crystallization exotherm of sPP#11 was found to locate at the highest temperature range, followed by that of sPP#14, sPP#10, sPP#13, sPP#12, and sPP#9, respectively. Based on the absolute temperature scale, sPP#11 showed the highest tendency to start crystallizing during a cooling scan. The ability of these resins to start crystallizing was found to be very similar when the difference in the equilibrium melting temperature of the resins was taken into account. The non-isothermal melt-crystallization kinetics of these sPP resins was well described by the Avrami, Urbanovici–Segal, Ozawa, and Ziabicki models. The subsequent melting behavior of these sPP resins exhibited either a single melting endotherm or double melting endotherms. 相似文献
Experimental miscibility studies were performed on different compositions of iPP/sPP blends, where sPP has a low syndiotacticity ([rrrr] = 81%). Combining optical microscopy, rheology, and solid state NMR spectroscopy, the miscibility of the blends was investigated at different scales in the traditionally thought to be "immiscible" iPP/sPP blends. For the composition of iPP/sPP (90/10) blend, it shows to be miscible in the melt, and furthermore, the existence of intermolecular chain interactions between sPP and iPP components was detected in the solid state. 相似文献
Summary: A series of polyethylene (PE) blends consisting of a high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) with a butene-chain branch density of 77/1000 carbon was prepared at different concentrations. The LLDPE only crystallized below 50 °C, therefore, above 80 °C and below the melting temperature of HDPE, only HDPE crystallized in the PE blends. A specifically designed multi-step experimental procedure based on thermal analysis technique was utilized to monitor the liquid–liquid phase separation (LLPS) of this set of PE blends. The main step was first to quench the system from the homogeneous temperatures and isothermally anneal them at a prescribed temperature higher than the equilibrium melting temperature of the HDPE for the purpose of allowing the phase morphology to develop from LLPS, and then cool the system at constant rate to record the non-isothermal crystallization. The crystallization peak temperature (Tp) was used to character the crystallization rate. Because LLPS results in HDPE-rich domains where the crystallization rates are increased, this technique provided an experimental measure to identify the binodal curve of the LLPS for the system indicated by increased Tp. The result showed that the LLPS boundary of the blend measured by this method was close to that obtained by phase contrast optical microscopy method. Therefore, we considered that the thermal analysis technique based on the non-isothermal crystallization could be effective to investigate the LLPS of PE blends. 相似文献
The epitaxial crystallization behavior of high-density polyethylene on the boundary of highly oriented isotactic polypropylene (iPP) substrates has been investigated by means of atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results obtained from AFM and TEM indicate that the epitaxial nucleation of HDPE on the highly oriented iPP substrates occurs earlier than that in the pure HDPE phase, i.e., homogeneous nucleation. Therefore the epitaxially grown HDPE lamellae can grow across the boundary of the iPP substrate into the HDPE spherulitic phase with the epitaxial orientation relationship remaining. 相似文献
The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate)(PBA) in poly(butylene succinate)(PBS)/poly(butylene adipate)(PBS/PBA) blends were studied by means of differential scanning calorimetry(DSC), wide-angle X-ray diffraction(XRD) and atomic force microscopy(AFM). It was revealed that the polymorphism of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α crystals, while low temperature contributes to edge-on β crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted. 相似文献
Titanium dioxide (TiO2) particles were introduced to improve the solar reflectance of high-density polyethylene (HDPE). The organic-inorganic hybrids were fabricated by melt blending. A series of characterizations were taken to study the crystallization behavior, morphology, solar reflectance, and real cooling property. TiO2 particles acted as nucleation agents in the HDPE matrix and made the HDPE form thick lamellar crystals. TiO2 particles could disperse well into the HDPE matrix under 2.5 wt.% loading but agglomerated with 3 wt.%. Solar reflectance was related to the reflective index of TiO2 and the microstructure of HDPE. The real cooling property depended on the solar reflectance and the dispersion of the TiO2 particles in the HDPE matrix. 相似文献