高强超韧高密度聚乙烯/聚丙烯共混物性能与微相分离结构的研究

在常规注射过程中 ,难以获得超高性能的共混体系注射制件 ,已有的研究表明 ,采用高剪切注射 ,可以抬高共混体系的最低临界相容温度曲线 (LCST)的位置 ,增加相容性 .当熔体进入模具后 ,冷却的同时相容性下降 ,开始相分离 ,相分离程度发展到某一程度即可获得高性能的制件 .对于高密度聚乙烯 (HDPE)、聚丙烯 (PP)两组分均为结晶型聚合物的共混体系 ,由于其相形态与结晶形态相互制约、竞争 ,微相分离程度难以控制 ,因此对其液 液相形态与结晶过程的控制是获得共混物最终形态与性能的关键 .采用振动保压注射成型技术不仅对HDPE、PP各自力学性能有明显的自增强作用 ,而且对HDPE/PP共混体系的力学性能也有十分明显的改善 .DSC、WAXD、SEM结果表明共混体系拉伸强度的提高主要取决于试样中串晶数量和大分子链的定向程度 ,而冲击强度则主要取决于两组分微观的相分离程度 .研究结果表明 ,HDPE/PP含量为 92 / 8的试样拉伸强度为 97 1MPa,80 / 2 0试样的缺口冲击强度为 4 5 5kJ/m2 ,较静态试样分别提高 4 3倍和 9 5倍 .采用振动填充注射技术针对某一组分可以获得高强度、高韧性的共混制件 .     

Study on the improvement of crystallization of high density polyethylene through dynamic packing injection molding

To better understand the effect of high‐density polyethylene on crystal morphology under the shear stress field, the dynamic packing injection molding was used to prepare the oriented pure polyethylene. In this present work, dynamic packing injection molding can exert a successive shear field on the melt in the mold cavity during packing stage. The structure of the samples was characterized through differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy. The oriented lamellae perpendicular to the flow direction can be formed. Oscillating stress between the lower and upper critical values can induce shish forming. The shish kebabs can be generated through sufficient relaxation led by slow cooling and suitable shear. We roughly discuss the relationship between the shear rate and crystal shape. Our results set up a method to reinforce polymer parts by regulating morphology and structure which can be used to do practical processing condition. Copyright © 2016 John Wiley & Sons, Ltd.     

SUPER POLYOLEFIN BLENDS ACHIEVED VIA DYNAMIC PACKING INJECTION MOLDING:MORPHOLOGY AND PROPERTIES

As a long-term project aimed at developing super polyolefin blends, in this paper we summarize our work on themechanical reinforcement and phase morphology of polyolefin blends achieved by dynamic packing injection molding(DPIM). The main feature of this technology is that the specimen is forced to move repeatedly in the model by two pistonsthat move reversibly with the same frequency during cooling, which results in preferential orientation of the dispersed phaseas well as the matrix. The typical morphology of samples obtained via DPIM is a shear-induced morphology with a core inthe center, an oriented zone surrounding the core and a skin layer in the cross-section areas. Shear-induced phase dissolutionat a higher shear rate but phase separation at low shear rates is evident from AFM examination of LLDPE/PP (50/50) blends.The super polyolefin blends having high modulus (1.9-2.2 GPa), high tensile strength (100-120 MPa) and high impactstrength (6 times as that of pure HDPE) have been prepared by controlling the phase separation, molecular orientation andcrystal morphology.     

Microstructure and mechanical properties of isotactic polypropylene composite with two‐scale reinforcement

Isotactic polypropylene (iPP) composite with two‐scale reinforcement structure, i.e. nanoscale shish–kebab structure and micron‐scale glass fiber (GF) with orientation, was fabricated by an oscillatory shear injection molding (OSIM) technology. The oscillatory shear flow provided by the OSIM gave rise to a high fraction of shish–kebab structures in the iPP composite, characterized by X‐ray scattering technique. On the other hand, the oscillatory shear flow oriented GFs in the iPP composite, which was revealed by scanning electron microscopy measurement. The iPP composite with this two‐scale reinforcement structure exhibited simultaneously remarkably enhanced tensile strength and impact strength. Fracture mechanism of this iPP composite was also proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

剪切作用下PA1010/PP共混物的形态与性能研究

通过动态保压注射成型方法制备了聚酰胺1010/聚丙烯(PA1010/PP)共混物,并研究了形态与性能的关系.力学性能测试结果表明在熔体冷却过程中施加剪切可以大大提高共混物的拉伸强度、拉伸模量和缺口冲击强度,当PP的质量分数为20%时,共混物的缺口冲击强度达到21.3kJ/m2,是静态样的3倍多,拉伸强度达到50.9MPa,是静态样的1.5倍.扫描电镜(SEM)结果表明在动态保压样的横断面可以观察到剪切诱导的形态,中间是芯层,围绕着芯层的是剪切层,最外面是皮层,相区尺寸显著减小、分散相分散更趋均匀,特别是PP的质量分数为20%时,相区尺寸从原来的约3.9μm降低到约1.4μm.动态保压样机械性能的提高归因于剪切作用下独特相形态的形成,分子链沿流动方向的取向是拉伸强度提高的主要原因,而剪切使分散相颗粒变小和剪切层中分子链的取向是冲击强度提高的主要原因.     

Molecular weight dependence of hybrid shish kebab structure in injection molded bar of polyethylene/inorganic whisker composites

In our previous work, a hybrid shish kebab structure, with polyethylene (PE) crystal lamellae periodically decorated on the surface of an inorganic whisker (SMCW) and aligned approximately perpendicular to the long axis of the whisker, has been observed in the injection molded bar of PE/SMCW composites. To investigate the effect of the molecular weight of the PE matrix on the formation of the hybrid shish kebab structure and the corresponding physical properties of HDPE/SMCW composites, in this work, three types of PE with different molecular weights were used to prepare the composites. They were first melt blended and then subjected to dynamic packing injection molding (DPIM), in which the prolonged shear was exerted on the melt during the solidification stage. An obvious hybrid shish kebab (HSK) structure, with PE crystal lamellae closely packed on the surface of the SMCW, was found in the samples with a low molecular weight PE (LMW-PE) matrix and a medium molecular weight PE (MMW-PE) matrix. However, in samples with a high molecular weight PE (HMW-PE) matrix, an incomplete HSK structure with PE crystal lamellae loosely decorated on the surface of the SMCW was observed. Furthermore, DSC results indicated that SMCW served as a good nucleating agent only for the composite with a LMW-PE matrix and the nucleation efficiency decreased with increasing PE molecular weight. Correspondingly, the tensile strength of the PE/SMCW composites was significantly improved by adding SMCW for the samples with a LMW-PE or MMW-PE matrix. Especially for samples with a LMW-PE matrix, the tensile strength was remarkably enhanced by the presence of only 1 wt % SMCW. For the composites with a HMW-PE matrix, the addition of SMCW had almost no reinforcing effect on the composites. The molecular weight dependence of the formation of HSK and property enhancement was discussed on the basis of the chain mobility and crystallization capability of the PE matrix.     

The interfacial enhancement of LLDPE/whisker composites via interfacial crystallization

Interfacial interaction plays a key role in the preparation of high performance polymer composites. In this work, in order to explore the possibility to enhance the interfacial interaction via interfacial crystallization of polymer matrix onto the filler surface, interfacial crystallization structure and mechanical properties of linear low density polyethylene (LLDPE)/whisker composites were investigated. The composites were firstly prepared by melt compounding, followed by processing in both traditional and dynamic injection molding. DSC, WAXD, SEM were used to characterize the interfacial crystallization structure. And the mechanical properties were measured by tensile testing. An imperfect shish‐calabash structure, with whisker served as shish, and irregular LLDPE spherulite as imperfect calabash, was formed during common injection molding processing. Such a structure was considered as the main reason for the strong interfacial adhesion and the obviously improved tensile strength and modulus. Furthermore, introducing shear could cause the formation of relatively perfect shish‐calabash structure, leading to the stronger interfacial adhesion. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

在低频振动场中注射成型HDPE试样的力学性能及其形态控制

利用自行研制的低频振动注射实验装置探讨HDPE振动注射试样力学性能和微观形态之间的关系 .实验中对常规注射和振动注射成型的试样力学性能和微观形态进行了对比实验 .SEM实验结果显示 ,振动注射制件芯层的形态由常规注射的球晶转变为垂直于振动波传递方向排列的片晶结构 ,在剪切层中同时存在串晶或柱状堆砌的片晶结构 .频率的改变 (0 相似文献   

Simultaneously Improving the Tensile and Impact Properties of Isotactic Polypropylene with the Cooperation of co-PP and β-nucleating Agent through Pressure Vibration Injection Molding

In this article, crystalline morphology and molecular orientation of isotactic polypropylene(i PP), random copolymerized polypropylene(co-PP) and ?-nucleating agent(?-NA) composites prepared by pressure vibration injection molding(PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and i PP molecular chains was beneficial for the mechanical improvement and the introduction of ?-NA further improved the toughness of i PP. In addition, after applying the pressure vibration injection molding(PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of i PP/co-PP/?-NA composites prepared by PVIM were simultaneously improved compared to those of the pure i PP prepared by conventional injection molding(CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of i PP/co-PP composites through dynamic processing strategy.     

Shear‐induced change of exfoliation and orientation in polypropylene/montmorillonite nanocomposites

For the improved dispersion of montmorillonite (MMT) in a polypropylene (PP) matrix, PP/MMT nanocomposites prepared via direct melt intercalation were further subjected to oscillating stress achieved by dynamic packing injection molding. The shear‐induced morphological changes were investigated with an Instron machine, wide‐angle X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The original nanocomposites possessed a partly intercalated and partly exfoliated morphology. A transformation of the intercalated structure into an exfoliated structure occurred after shearing, and a more homogeneous dispersion of MMT in the PP matrix was obtained. However, the increase of the exfoliated structure was accompanied by the scarifying of the orientation of MMT layers along the shear direction. Some bended or curved MMT layers were found for the first time by TEM after shearing. However, the orientation of PP chains in the PP/MMT nanocomposites became very difficult under an external shear force; this indicated that the molecular motion of PP chains intercalated between MMT layers was highly confined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1–10, 2003     

Unexpected molecular weight dependence of shish-kebab structure in the oriented linear low density polyethylene/high density polyethylene blends

In this study, highly oriented shish-kebab structure was achieved via imposing oscillatory shear on the melts of linear low density polyethylene (LLDPE)/high density polyethylene (HDPE) blends during the packing stage of injection molding. To investigate the effect of molecular weight of HDPE on the formation of shish-kebab structure, two kinds HDPE with large melt flow index (low molecular weight) and small melt flow index (high molecular weight) were added into LLDPE matrix. The structural characteristics of LLDPE/HDPE blends were systematically elucidated through two-dimensional wide-angle x-ray scattering, scanning electron microscopy, and differential scanning calorimetry. Interestingly, an unexpected molecular weight dependence of shish-kebab structure of the prepared samples was found that the addition of HDPE with low molecular weight resulted in an higher degree of orientation, better regularity of lamellar arrangement, thicker lamellar size, and higher crystal melting temperature than that adding HDPE with high molecular weight. Correspondingly, the blend containing low molecular weight HDPE had better tensile strength. A possible mechanism was suggested to elucidate the role of HDPE molecular weight on the formation of shish-kebab structure in the oriented blends, considering the change of chain mobility and entanglement density with change of molecular weight.     

常压动态保压注塑自增强高密度聚乙烯的结构与性能

研究了常压动态保压注塑自增强高密度聚乙烯的结构和力学性能的关系,自增强高密度聚乙烯的抗张强度和杨氏模量分别从原来的23MPa和1.0GPa提高到93MPa和5.0GPa。DSC、TEM和X射线衍射研究结果表明:力学性能的显著改善主要归因于串晶的产生、高分子链沿流动方向的轴取向和结构更加完善的球晶的生成。和高压保压法相比,本法具有现实的工业应用前景。     

HDPE/PP共混物在振动剪切作用下的力学性能与形态控制

采用高剪切引起的相容与振动剪切保压方式控制共混物的形态,结果表明,当共混体系中HDPE/PP为92/8时的试样拉伸强度为97.1MPa,而80/20试样的缺口冲击强度为45.5kJ/m₂,较静态试样分别提高4.3倍和9.5倍.采用振动剪切注射技术可以针对某一组分获得高强度、高韧性的HDPE/PP共混制件.     

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002     

The effect of shear on mechanical properties and orientation of HDPE/mica composites obtained via dynamic packing injection molding (DPIM)

The interfacial interaction and orientation of filler play important roles in the enhancement of mechanical performances for polymer/inorganic filler composites. Shear has been found to be a very effective way for the enhancement of interfacial interaction and orientation. In this work, we will report our recent efforts on exploring the development of microstructure of high density polyethylene (HDPE)/mica composites in the injection‐molded bars obtained by so‐called dynamic packing injection molding (DPIM), which imposed oscillatory shear on the melt during the solidification stage. The mechanical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA), and the crystal morphology, orientation, and the dispersion of mica were characterized by scanning electron microscopy and two‐dimensional wide‐angle X‐ray scattering. Compared with conventional injection molding, DPIM caused an obvious increase in orientation for both HDPE and mica. More importantly, better dispersion and epitaxial crystallization of HDPE was observed on the edge of the mica in the injection‐molded bar. As a result, increased tensile strength and modulus were obtained, accompanied with a decrease of elongation at break. The obtained data were treated by Halpin–Tsai model, and it turned out that this model could be also used to predict the stiffness of oriented polymer/filler composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Shear‐Induced Morphological Change in PP/LLDPE Blend

The morphology of a PP/LLDPE blend (50 : 50) by phase dissolution at high shear rate combined with dynamic packing injection molding at low shear rate was investigated by atomic force microscopy. Phase dissolution under high shear rate is manifested by a co‐continuous two‐phase structure that could be broken down to an island‐like structure when a low shear rate is applied via dynamic packing injection molding or simply by manual deformation.     

聚烯烃共混物注射制品的形态控制与多层次结构

从注射制品形态控制和结构表征的角度探讨高分子材料加工-形态-性能之间的关系.研究中采用动态保压成型方法来制备注射样品,在注射成型过程中引入剪切应力场的作用,制得的样品表现出明显的多层次结构,从外向里分别为皮层、剪切层、芯层,表现出不同的相形态、结晶形貌以及取向行为.研究发现,剪切应力对聚烯烃的形态发展和结构变化具有重要影响.在剪切应力的作用下,聚烯烃共混物中分散相会发生变形、取向,从而导致共混物的相转变点发生移动;结晶形态从球晶转变为shish-kebab结构;聚烯烃共混物在高剪切应力下相容,低剪切下发生相分离;HDPE/PP共混物的注射制品中出现附生结晶等现象.     

A novel hierarchical crystalline structure of injection-molded bars of linear polymer: co-existence of bending and normal shish–kebab structure

The hierarchy structures and orientation behavior of high-density polyethylene (HDPE) molded by conventional injection molding (CIM) and gas-assisted injection molding (GAIM) were intensively examined by using scanning electronic microscopy (SEM) and 2D wide-angle X-ray diffraction (2D-WAXD). Results show that the spatial variation of crystals across the thickness of sample molded by CIM was characterized by a typical skin–core structure as a result of general shear-induced crystallization. Unusually, the crystalline morphologies of the parts prepared by GAIM, primarily due to the penetration of secondary high-compressed gas that was exerted on the polymer melt during gas injection, featured a richer and fascinating supermolecular structure. Besides, the oriented lamellar structure, general shish–kebab structure, and common spherulites existed in the skin, sub-skin, and gas channel region, respectively; a novel morphology of shish–kebab structure was seen in the sub-skin layer of the GAIM parts of HDPE. This special shish–kebab structure (recognized as “bending shish–kebab”) was neither parallel nor perpendicular to the flow direction but at an angle. Furthermore, there was a clear interface between the bending and the normal shish–kebab structures, which may be very significant for our understanding of the melt flow or polymer rheology under the coupling effect of multi-fluid flow and complex temperature profiles in the GAIM process. Based on experimental observations, a schematic illustration was proposed to interpret the formation mechanism of the bending shish–kebab structure during GAIM process.     

Combined Effects of Stretching and Nanofillers on theCrystalline Structure and Mechanical Properties ofPolypropylene and Single-walled Carbon NanotubeComposite Fibers简

The combined effects of stretching and single-walled carbon nanotubes （SWCNTs） on crystalline structure and mechanical properties were systematically investigated in melt-spun polypropylene （PP） fibers prepared at two different draw ratios. The dispersion, alignment of the SWCNT bundles and interfacial crystalline structure in the composite fibers are significantly influenced by the stretching force during the melt spinning. The nanohybrid shish kebab （NHSK） superstructure where extended PP chains and aligned SWCNT bundle as hybrid shish and PP lamellae as kebab has been successfully obtained in the composite fibers prepared at the high draw ratio and the related formation mechanism is discussed based on the results of morphological observations and 2d-SAXS patterns. Large improvement in tensile strength and modulus has been realized at the high draw ratio due to the enhanced orientation and dispersion of SWCNT bundles as well as the formation of NHSK.