Mechanical behavior of CaCO3 particulate-filled β-crystalline phase polypropylene composites

β-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30, and 40% (by weight) of CaCO₃ filler were prepared by injection molding. The β-form PP was produced by adding a bicomponent β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The morphology, static tensile, and impact properties of these composites were investigated in this study. Scanning electron microscopy (SEM) observations revealed that the β-spherulites of the polymer matrix of the composites exhibit curved lamellae and sheaf-like structures. The fillers were observed to disperse within the inter-lamellar spacings of the β-PP composite containing 10% calcium carbonate addition. However, the filler particles tend to link together to form larger aggregates when the filler content reaches 20%. Static tensile measurements showed that the elastic modulus of the composites increases with increasing filler content but the yield strength decreases with increasing filler addition. The falling weight Charpy impact test indicated that the β-PP polymer exhibits the highest critical strain energy release rate (G_c) value. However, there was a drastic drop in G_c of the β-PP composites with increasing filler content. The results are discussed and explained in terms of materials morphology.     

Non-isothermal crystallization kinetics of calcium carbonate-filled β-crystalline phase polypropylene composites

The non-isothermal crystallization behaviour of high purity β-phase and α-phase polypropylene (PP) and their calcium carbonate-filled composites was investigated by means of differential scanning calorimetry. High purity β-PP polymer was prepared by adding an effective β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The crystallization temperature and crystallization rate coefficient of pure β-PP polymer were considerably higher than those of the α-PP polymer. This was due to the β-PP polymer containing nucleating agents, which act as nuclei for β-spherulites. The calcium carbonate content had little or no effect on the crystallization rate coefficient and Ozawa exponent of the β-phase PP in the composites. On the other hand, the crystallization temperature, crystallization rate coefficient and Ozawa exponent of the α-phase PP composites depended on the calcium carbonate loading. The effect of calcium carbonate additions on the crystallization of α-PP and β-PP is discussed. ©1997 SCI     

Mechanical properties and impact toughness of talc-filled β-crystalline phase polypropylene composites

Injection molded β-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30 and 40% (by weight) of talc filler were studied by X-ray diffraction, scanning electron microscopy, static tensile and falling drop weight impact tests. The X-ray diffraction analysis showed that the talc filler suppresses the formation of β-form PP dramatically. As a result, the β-PP composites containing talc content ≥20 wt% consisted mainly of the α-form PP phase. The tensile test showed that the addition of talc filler up to 40 wt% leads to an increase in Young's modulus whereas little effect is observed on the yield strength of composites with the addition of talc up to 30%. This behavior can be attributed to the load bearing effect of talc particles with a platelike structure and to good interfacial bonding exists between the matrix and filler. The impact tests revealed that the critical stain energy release rate (G_c) of the β-PP polymers appears to increase initially with the addition of 5 wt% talc; thereafter it decreases significantly with increasing talc content.     

Bamboo fiber-reinforced polypropylene composites: Crystallization and interfacial morphology

Bamboo fiber-reinforced polypropylene (PP) composites were prepared. PP and two maleated polypropylenes (s-MAPP and m-MAPP) were used as matrices. Crystallization and interfacial morphology were studied by using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and optical microscopy. It has been shown that the addition of bamboo fiber to any of the three polymers causes an increase in the overall crystallization rate. A considerable amount of β-form crystallinity was produced in the PP, s-MAPP, and m-MAPP by mixing with bamboo fiber; and all the bamboo fiber-filled samples contain both the α- and the β-forms. The relative amount of the β-form in the samples was calculated from WAXD data by the K value. There is no β-form observed in the pure PP, s-MAPP, and m-MAPP. Bamboo fiber acted as both a reinforcement and a β-nucleator. The nucleation density of both s-MAPP and m-MAPP at the fiber surface is remarkably higher than that of PP because an improved interfacial adhesion is reached in the case of s-MAPP and m-MAPP as matrices. The transcrystalline growth of s-MAPP and m-MAPP on the bamboo fiber surface was observed under optical microscope with crossed polars. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1267–1273, 1997     

Effect of Vibrating Extrusion on the Structure and Mechanical Properties of Isotactic Polypropylene

An electromagnetic dynamic plasticating extruder, invented by the authors, was used to prepare isotactic polypropylene (PP) sheets. Tensile and impact tests show that the extruded samples can simultaneously be reinforced and toughened along the flow and transverse directions in a moderate frequency and amplitude range. The microstructures of the obtained samples were characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and scanning electron microcopy (SEM). The results indicate that the vibration plasticating extrusion affected the morphology of the PP extrudate, it especially resulted in finer spherulites, and move tie molecules, which account for the enhancement of the tensile strength and impact toughness of PP sheets in both extrusion and transversal directions.     

A study on the photo-degradation of zinc oxide (ZnO) filled polypropylene nanocomposites

This research aims to study the photo-degradation characteristics for zinc oxide (ZnO) nanoparticle filled polypropylene (PP) nanocomposites. By paying attention to the evolution of the carbonyl absorption bands from FTIR analysis, it has been observed that UV irradiation induced significant photo-degradation for unfilled PP. However, with the incorporation of ZnO nanoparticles into the PP matrix, the extent of photo-degradation was significantly reduced. This is due to the superior UV light screening effects offered by the ZnO nanoparticles. WAXD measurements showed that β-form PP crystal had been induced in the PP/ZnO nanocomposites. An interesting observation from this study is that β-form PP crystal was also induced in unfilled PP due to UV irradiation. UV-irradiation induced degradation caused a significant drop in the ductility for unfilled PP. With the incorporation of ZnO nanoparticles, the ductility, and hence the tensile strength were recovered to some extent. The higher the ZnO particle content, the higher the elongation at break value in the UV irradiation treated nanocomposites. It was also observed that surface cracks were induced by photo-degradation, and the Talysurf surface profile measurements indicate that the severity of the surface cracks were significantly reduced in the ZnO/PP nanocomposites.     

Mechanical properties and structural characteristics of dynamically photocrosslinked PP/EPDM blends

The mechanical properties and crystal morphological structures of dynamically photocrosslinked polypropylene (PP)/ethylene‐propylene‐diene terpolymer (EPDM) blends have been studied by mechanical tests, wide‐angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Dynamically photocrosslinking of PP/EPDM blends can improve the mechanical propertiess considerably, especially the notched Izod impact strength at low temperature. Data obtained from mechanical tests show that the notched Izod impact strength of a dynamically photocrosslinked sample with 30% EPDM at ?20°C is about six times that of an uncrosslinked sample with the same EPDM component. The results from the WAXD, SEM, and DSC measurements reveal the enhanced mechanism of impact strength for the dynamically photocrosslinked PP/EPDM blends as follows: (i) the β‐type crystal structure of PP is formed and the interplanar distance of β‐type crystal increases slightly with an increase in the EPDM component; (ii) the droplet size of the EPDM phase in the photocrosslinked PP/EPDM blends is obviously reduced and the droplet number is increased with an increase in the EPDM component during the dynamical photocrosslinking process; (iii) the graft copolymer of PP‐g‐EPDM is formed at the interface between PP and EPDM components. All the above changes from the crystal morphological structures are favorable for increasing the compatibility and enhancing the toughness of PP/EPDM blends at low temperatures.     

乙烯含量对无规共聚聚丙烯晶型及性能影响的研究

通过差示扫描量热分析、X射线衍射分析以及力学性能测试等方法,研究了不同乙烯含量的无规共聚聚丙烯（PPR）体系中,在添加定量β成核剂的条件下,乙烯含量对PPR结晶行为及热学、力学性能的影响。结果表明,PPR的熔点和结晶温度都随其乙烯含量的减少而升高;乙烯含量较少的体系,有利于β晶的形成;体系中β晶含量的提高,会使样品热变形温度提高,且冲击性能显著增强;乙烯含量的提高,增大了PPR β结晶的调控难度;实验室自制β成核剂,可使乙烯含量为0.25 %~5.1 %（质量分数,下同）的PPR中的β晶含量达到80 %以上。     

Preparation and structural study of polypropylene–talc gradient materials

Polypropylene (PP)–talc composites with proper spatial gradients were prepared by gradually varying the component ratio of PP and talcum powder during the extrudion process. The gradient variations of composition, structural and physical properties along the radius direction of a cylindrical sample were studied by wide angle x‐ray diffraction (WAXD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and tensile testing. The WAXD and TG results indicate that the content of either component shows a monotonic change along the radius direction. With increasing radius, a gradually decreased percentage of PP was observed, while that of the talc filler gradually increased. A gradually varying stacking density of the talcum powder in the PP matrix was also observed by the SEM images for the sliced specimens sampled at different positions. As a result of such variations in both component and structure, the physical properties, including the mechanical performance and thermal behaviour of the PP–talc composites, gradually varied along the radius direction. The experimental data show that a polymeric gradient material (PGM), with significantly different structures and properties existing on both sides, can be prepared by using this unique process. Copyright © 2004 Society of Chemical Industry     

稀土β成核剂在聚丙烯中的应用

采用偏光显微镜(PLM)、差示扫描量热仪(DSC)、广角X射线衍射仪(WAXD)等研究了一种稀土类β成核剂WBG对等规聚丙烯( iPP)性能的影响。结果表明,加人WBG可诱导PP中a晶型的生成。当WBG加人量为0.2%时,β晶型的含量可达57%。加人少量WBG,均聚聚丙烯悬臂梁冲击强度提高1.48倍,热变形温度提高11一31℃。在制品成型过程中,较慢的冷却速率有利于β晶的生成和完善。制品成型后,后期热处理有利于试样综合性能进一步提高,最佳处理温度为100 C o PLM发现了一种新现象:中心β晶呈树叶状生长,当晶体长到一定尺寸后,中心外缘附生舀球晶,β球晶之间形成比纯PP小且不规则的界面,部分中心β晶相互贯穿。     

新型α和β成核剂对PP结晶和力学性能的影响

在聚丙烯(PP)中加入两种新型成核剂:二苄叉山梨醇衍生物YS-688(α成核剂)和芳酰胺类化合物TMB-5(β成核剂),通过密炼–挤出的方法制备了PP/成核剂共混物材料。通过偏光显微镜、X射线衍射、差示扫描量热和力学性能测试研究了这两种成核剂对共混物结晶和力学性能的影响。结果表明,两种成核剂在适量时均能提高PP的结晶速率和结晶度,细化晶粒,且使晶体界面模糊,其中TMB-5具有较强的诱导PPβ晶成核的能力,当其质量分数为0.075%时,可使PP形成树枝状的β晶,而YS-688未改变PP的晶型,只生成了α晶。YS-688可提高共混物的拉伸强度,而TMB-5对共混物的拉伸强度影响很小;当两种成核剂质量分数均为0.075%时,共混物的韧性最好,相对于纯PP,PP/YS-688共混物的常温和–30℃缺口冲击强度分别提高了37.41%和12.76%,拉伸强度提高了11.11%;PP/TMB-5共混物的常温和–30℃缺口冲击强度分别提高了100%和55.41%。     

Instrumented tensile and falling weight impact response of injection-molded α- and β-phase polypropylene homopolymers with various melt flow indices

In this study the instrumented tensile (ITI) and falling weight impact (IFWI) behavior of injection-molded α- and β-phase polypropylene (PP) homopolymers were compared at ambient temperature in a broad melt flow index (MFI = 0.7–13 dg/min) range. It was found that the toughness of β-PP is superior to the α-PP: the difference between them increased with decreasing MFI or increasing molecular weight (MW). As expected, the injection molding induced skin layer thickness increased with increasing MW. Effects of the skin-core morphology were deduced indirectly by considering the results achieved on specimens molded at low and high injection speeds (v_inj = 6 and 150 mm/s), respectively. It was found that the effect of the skin-core structure is markedly stronger under uniaxial in-plane (i.e., ITI) than in biaxial out-of-plane type loading (i.e., IFWI). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1205–1214, 1999     

Self-Reinforced Isotactic Polypropylene Prepared by Melt Vibration Injection Molding

Polypropylene (PP) has a good combination of properties, but at low temperatures it is friable and its impact ductility is very low. To improve impact strength, a vibration injection molding (VIM) technology was used to investigate the mechanical properties of polypropylene. Yield strength is upgraded with an increment in vibration frequency and a peak stands at a special frequency for VIM; the elongation at break and impact strength are also enhanced by increased vibration frequency. The wide-angle x-ray diffraction (WAXD) curves and the scanning electronic microscopy (SEM) micrographs have shown that, in the vibration field, the enhancement of mechanical properties is attributed to the occurrence of γ-phase crystals and more pronounced spherulite deformation than those seen in conventional injection moldings (CIM), and the smaller spherulites with the existence of β-phase crystals are favored for improving toughness. With the application of vibration injection molding, the mechanical properties of isotactic PP are improved. To prepare self-reinforcing and self-toughening polypropylene molded parts it has been concluded that high vibration frequency is required. Increasing vibration pressure amplitude obviously significantly improves the yield strength and impact strength.     

Exploring the roles of molecular structure on the β-crystallization of polypropylene random copolymer

To investigate effects of molecular structures on β-crystallization of polypropylene random copolymer (PPR), PPR-A and PPR-B with similar molecular weight and distribution but significantly different polymorphic behavior were used. Wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FT-IR), solvent fractionation combined with successive self-nucleation and annealing (SSA) and Gel Permeation Chromatography (GPC) were applied. Results revealed that after addition of same amount of β-nucleating agent (β-NA), large amount of β-phase is obtained in PPR-A (K _β  = 0.603), while no β-phase can be seen from PPR-B; Structure characterizations revealed that they have similar molecular weight but different total amount and distribution of ethylene comonomer: the total content of ethylene comonomer of PPR-A is higher compared with PPR-B, but its ethylene comonomer distribution is less uniform. In this way, PPR-A possesses high molecular weight high isotactic fraction, which cannot be seen from PPR-B due to its more uniform comonomer distribution. Therefore, the presence of highly isotactic PP (HPP) is the key factor in β-crystallization of PPR. For verification, HPP with low or high molecular weights are respectively added into β-nucleated PPR-B. Results revealed that HPP was effective in enhancing β-crystallization of PPR-B; higher molecular weight of HPP was more favorable and more effective.     

Effective reinforcement of carbon nanotubes in polypropylene matrices

This study describes an attempt to mechanically reinforce polypropylene (PP) using multi‐wall carbon nanotubes (MWNTs) through a melt compounding process followed by hot‐pressing and solid state drawing. The effect of a high density polyethylene (HDPE) coating on MWNTs and melt flow index (MFI) of PP on the dispersion of MWNTs and composite properties are studied by means of mechanical tests, transmission electron microscopy (TEM), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and wide angle x‐ray diffraction (WAXD). Highly orientated composite tapes are prepared to fully utilize the properties of MWNTs in uniaxial direction. Highly aligned MWNTs are shown by SEM, while highly oriented polymer chains are characterized by WAXD. Composite theory is used to analysis the results and indicate that effective reinforcement of PP by MWNTs is highest at relatively low filler content and draw ratios. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

冷却温度对聚丙烯薄膜结晶、形态和拉伸性能的影响

采用示差扫描量热法(DSC)、广角X射线衍射(WAXD)和扫描电镜(SEM)对聚丙烯(PP)薄膜的结晶、形态进行了研究,并测试了薄膜的拉伸性能.结果表明:冷却水温度变化对生产PP薄膜的结晶、形态和拉伸性能有很大影响.在冬季,PP薄膜的结晶度更小,晶体尺寸更均一;但在夏季,PP薄膜的拉伸强度、杨氏模量和断裂伸长率分别提高45%、85%和94%.最后,通过数值模拟,得到了给定条件下相关冷却参数的合理数值.     

Miscibility,Mechanical and Thermal Properties of Melt-Mixed Poly(trimethylene terephthalate)/Polypropylene Blends

This study examined the miscibility, mechanical and thermal properties of melt-mixed blends of PTT(poly(trimethylene terephthalate)) with PP(isotatic polypropylene). DMA and SEM results indicated that the PTT/PP blends are immiscible. Revealed from TGA analyses, the blends with a higher PP content showed a higher degradation temperature. A complex melting behavior was observed for the blends. The isothermal crystallization kinetics of the blends was analyzed from 200°C to 210°C using the Avrami equation. The WAXD results showed that the crystal structure of PTT remained unchanged in the blends. Nevertheless, the PP rich blends possessed lower tensile strength and higher elongation at break.     

β成核剂和纳米SiO_2复合改性PP/POE复合材料研究

研究了纳米SiO2和β成核剂对PP/POE复合材料力学性能的影响,并用广角X射线衍射仪(WAXD)对其进行了表征。结果表明:纳米SiO2的加料方式影响PP/POE复合材料的力学性能,先将PP和纳米SiO2共混挤出,再与POE共混制备得到的复合材料冲击强度最高。当纳米SiO2含量为4%时,PP/POE/纳米SiO2复合材料的综合力学性能最好。在PP/POE/纳米SiO2复合体系中的加入β成核剂后,复合材料的拉伸强度和弯曲强度下降,而韧性进一步提高,当β成核剂含量为0.4%时,复合材料的缺口冲击强度和断裂伸长率达到最大值,拉伸强度也明显提高。XRD表明,β成核剂在纳米SiO2改性PP/POE复合体系中能显著诱导β晶的生成。     

流动场下含β成核剂的玻璃纤维增强聚丙烯复合材料结构与性能研究

采用普通注射成型和动态保压注射成型分别制备了不同玻璃纤维（GF）含量和β成核剂含量的等规聚丙烯（iPP）复合材料,测试了复合材料的力学性能,并采用二维广角X射线衍射、扫描电子显微镜和二维小角X射线散射研究了复合材料的iPP分子链取向、GF取向及结晶性能。结果表明,在动态保压注射成型条件下,GF含量为30 %（质量分数,下同）、β成核剂含量为0.2 %时,复合材料具有最优异的综合性能,拉伸强度为58.52 MPa,冲击强度为9.26 kJ/m2,这是由于在流动场下含GF与β成核剂的复合材料形成了"皮刚芯韧"类竹子的仿生结构。     

Orientation in polypropylene sheets produced by die-drawing and rolling

Two orienting techniques for stiffening semicrystalline polymers, rolling and die-drawing, are compared with respect to the anisotropy they produce in isotactic polypropylene (PP). Billets of PP were either drawn at 145°C through a tapered slotted die in the Leeds large-scale die-drawing machine to reduction ratios R of 2.2, 5.1 and 7.6, or rolled between rolls of 65 mm diameter at 120°C to R = 2 to 5. Drawing increased the crystallinity, as estimated from differential scanning calorimetry, density and wide-angle X-ray diffraction (WAXD); it thus disrupts the original PP structure, developing an oriented crystalline structure. WAXD pole figures showed that both die-drawing and rolling oriented the molecular chain axis nearly parallel to the machine direction and the b axis perpendicular to the drawing plane. This approximate uniaxial symmetry was confirmed by ultrasonic measurements of the stiffness matrix. In tensile and falling-dart impact tests, samples failed by delaminating in the drawing plane. Although stresses are applied to the material in quite different ways in die-drawing and in rolling, the geometry of deformation in both is similar, close to plane strain.