热致液晶共聚酯对聚丙烯结晶的诱导作用

用差示扫描量热法和光学解偏振法研究了热致液晶性芳香共聚酯与聚丙烯共混物的等温和非多温结晶行为.结果表明,这一热致液晶聚合物对聚丙烯结晶有诱导成核和加速作用.当共聚酯含量在2-5％之间时,聚丙烯的结晶速率最快.偏光显微镜的观察揭示出在聚丙烯熔体中原位形成的液晶聚合物微纤诱导了聚丙烯横穿晶的形成.     

水辅助注塑PP/SAN共混物制品中横晶形成机理的研究

采用水辅助注塑(WAIM)设备,在不同的注水压力和熔体温度下制备了4种质量比(98/2,96/4,94/6和92/8)的聚丙烯/丙烯腈-苯乙烯共聚物(PP/SAN)共混物制品.采用偏光显微镜(POM)和扫描电子显微镜(SEM),研究了WAIM PP/SAN共混物制品的结晶形态和相形态.研究发现,高压水的穿透作用所引起的强剪切和快速冷却可诱导SAN在PP基体中原位成纤,并诱导PP在SAN纤维表面形成大量的晶核而最终形成横晶.SAN含量为4 wt%时,所形成横晶的含量随水压的提高而增加,随温度的降低而大幅增加.当SAN含量较低(2 wt%)时,制品中没有横晶形成.     

A comparison study on the homogeneity and heterogeneity fiber induced crystallization of isotactic polypropylene

The crystallization behavior of iPP in composites with PET, Nylon-6 and its own fibers under various conditions was studied using an optical microscope equipped with a hot stage. The results show that the nucleation capacity of PET and Nylon-6 fibers towards the iPP matrix is mainly controlled by the shear flow of the iPP matrix during sample preparation. When the composites were prepared at a temperature where the iPP was kept in its supercooled state, the nucleation of iPP on the PET and Nylon-6 fiber surfaces was enhanced due to the shearing of the iPP melts caused by introduction of the fibers. The nucleation was markedly reduced by keeping the composites at the fiber introduction temperature for a short time to relax the shear flow of the iPP matrix. The nucleation of iPP on its own fiber, however, is mainly related to the nature of the iPP fiber itself. No detectable morphological change of iPP on its own fiber can be identified under all thermal conditions used in this study.     

SPATIAL HIERARCHY AND INTERFACIAL STRUCTURE IN INJECTIONMOLDED BARS OF POLYPROPYLENE-BASED BLENDS AND COMPOSITES

The hierarchical structure and interfacial morphology of injection-molded bars of polypropylene （PP） based blends and composites have been investigated in detail from the skin to the core. For preparation of injection-molded bars with high-level orientation and good interfacial adhesion, a dynamic packing injection molding technology was applied to exert oscillatory shear on the melts during solidification stage. Depending on incorporated component, interfacial adhesion and processing conditions, various oriented structure and morphology could be obtained. First, we will elucidate the epitaxial behavior between PP and high-density polyethylene occurring in practical molded processing. Then, the shear-induced transcrystalline structure will be the main focus for PP/fiber composites. At last, various oriented clay structures have been ascertained unambiguously in PP/organoclay nanocomposites along the thickness of molded bars.     

Effects of matrix molecular weight on structure and reinforcement of high density polyethylene/mica composites

Three types of high-density polyethylene(HDPE)with different molecular weights(high,medium and low)were adopted to evaluate the influence of matrix molecular weight on the structure-property relation of injection-molded HDPE/mica composites through a combination of SEM,2d-WAXS,DSC,DMA and tensile testing.Various structural factors including orientation,filler dispersion,interfacial interaction between HDPE and mica,etc.,which can impact the macroscopic mechanics,were compared in detail among the three HDPE/mica composites.The transcrystallization of HDPE on the mica surface was observed and it exhibited strong matrix molecular weight dependence.Obvious transcrystalline structure was found in the composite with low molecular weight HDPE,whereas it was hard to be detected in the composites with increased HDPE molecular weight.The best reinforcement effect in the composite with low molecular weight HDPE can be understood as mainly due to substantially improved interfacial adhesion between matrix and mica filler,which arises from the transcrystallization mechanism.     

CRYSTALLIZATION IN PARTIALLY MOLTEN ORIENTED BLENDS OF POLYCONDENSATES AS REVEALED BY X-RAY STUDIES*

Oriented fibers or films of binary polymer blends from polycondensates were investigated by two-dimensional (2D) wide-angle X-ray scattering (WAXS) during the finishing process of microfibrillar reinforced composite (MFC) preparation, that is, heating to a temperature between the melting temperatures of the two components, isothermal annealing, and subsequent cooling. It is shown that the crystallization behavior in such MFC from polycondensates depends not only on the blend composition, but also on thermal treatment conditions. Poly(ethylene terephthalate)/polyamide 12 (PET/PA12), poly(butylene terephthalate)/poly(ether ester) (PBT/PEE), and PET/PA6 (polyamide 6) composites were prepared in various compositions from the components. Materials were investigated using rotating anode and synchrotron X-ray source facilities. The effect of the annealing time on the expected isotropization of the lower melting component was studied in the PET/PA6 blend. It was found that PA6 isotropization took place after 2 h; shorter (up to 30 min) and longer (up to 8 h) melt annealing results in oriented crystallization due to different reasons. In PET/PA12 composites, the effect of PA12 transcrystallization with reorientation was confirmed for various blend compositions. The relative strength of the effect decreases with progressing bulk crystallization. Earlier presumed coexistence of isotropic and highly oriented crystallites of the same kind with drawn PBT/PEE blend was confirmed by WAXS from a synchrotron source.

     

Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

The effect of fibre treatments on thermal stability of flax fibre and crystallization of flax fibre/polypropylene composites was investigated. For thermal stability study, flax fibres have been treated using maleic anhydride, maleic anhydride polypropylene copolymer, vinyltrimethoxy silane and alkalization. In order to compare thermal stability of flax fibres thermogravimetry (TG) analysis has been used. Kinetic parameters have been determined by Kissinger method. Results showed that all treatments improved thermal stability of flax fibres. For crystallinity analysis, three different techniques have been used, differential scanning calorimetry analysis (DSC), pressure–volume–temperature (PVT) measurements for analysis of volume shrinkage and polarized optical microscopy (POM). All techniques results showed that addition of flax fibre increased crystallization rate. Besides, depending on fibre surface treatment and crystallization temperature, flax fibre/PP composites can show transcrystallinity.     

INTERNAL STRUCTURE OF CO-INJECTION MOLDED PP/PP SPECIMEN

An overview of the microstructural characteristics of co-injection molded isotactic polypropylene products is given. Polarized light optical microscopy is used for comparison of traditional injection molded and co-injection molded products' microstructure. It is shown that a transcrystalline layer occurs on the boundary of the skin and the core components when a nucleation agent was added to either of the components; this proves that this surface layer is not shear induced cylindritic structure. Also shown is a method for preparing β-phase transcrystalline structure capitalizing on the advantages of the co-injection molding technology.     

Effect of annealing on the structure of quenched isotactic polypropylene

Smectic isotactic polypropylene films were annealed at different temperatures for different times. Density, wide-angle x-ray scattering (WAXS), differential scanning calorimetry, and the transport properties of methylene chloride vapor were used to follow the transformation of the smectic phase into the monoclinic phase. The results of WAXS diffractograms indicate different saturation levels of crystallization with the maximum order attained progressively more quickly at higher temperatures. Density measurements, however, show that, after a first saturation level, a further increase of this parameter occurs after long annealing times; and this second step is lower, the higher the temperature. Sorption and diffusion, analyzed to investigate the amorphous component, show that annealing the smectic phase at 50°C results in a decrease of amorphous fraction without transformation of the smectic phase. The transition from smectic to monoclinic phase occurs at temperatures higher than 60°C. During the annealing at 80°C there is first a decrease of amorphous fraction corresponding to the first saturation level of the density, and then a further decrease of amorphouse phase corresponding to the final increase of density after 24 hr of annealing.     

The synergetic effect of zinc phthalate and carboxymethyl cellulose–carbon nanotube of glass fibers surfaces on improving strength and toughness of polypropylene composite

The interfacial interaction between glass fibers (GFs) and polypropylene (PP) resin is the key factor which affects the properties of GFs reinforced PP composites. The β-transcrystallization (β-TC) structure induced by β-nucleating agent (β-NA) at the interface is beneficial to improving the interfacial performance and comprehensive mechanical properties. However, due to the poor adhesive ability, it is difficult to introduce β-NAs onto GFs surface directly. In this work, for solving above problem, the sodium carboxymethyl cellulose (CMC) and  NH₂ functionalized multiwalled carbon nanotubes (CNTs) were used to construct the network structure on GFs (CMC-CNT-GF) through plenty of active groups. Furthermore, the zinc phthalate (ZnPht, β-NA) was synthesized and coated on GFs surface by hydrogen bonds interaction with CMC-CNT and physical anchoring effect (ZnPht@CMC-CNT-GF). Finally, the hybrid GFs reinforced PP composite (iPP/ZnPht@CMC-CNT-GF) was prepared, which exhibited enhanced tensile, flexural, and impact strength by 20.1, 9.3, and 33.3%, respectively when compared with the iPP/raw GF due to the formation of β-TC and improvement of interfacial adhesion. This study provides an effective strategy to introduce β-NAs on GFs with network structure for improving interfacial properties by inducing β-TC to enhance the strength and toughness of composite, which could be applied in other fiber/semicrystalline polymer systems.